OVERVIEW OF THE GUIDELINES
The ACS publishes Nutrition and Physical Activity Guidelines to advise health care professionals and the general public about dietary and other lifestyle practices that reduce cancer risk.9,10 These Guidelines, updated in 2006 by the ACS Nutrition and Physical Activity Guidelines Advisory Committee, are based on synthesis of the current scientific evidence on diet and physical activity in relation to cancer risk. The Committee reviewed evidence from human population studies and laboratory experiments published since the last release of the Guidelines in 2001. The Committee also considered other comprehensive reviews of diet, obesity, and physical inactivity in relation to cancer. For some aspects of nutrition, the most thorough review was the 1997 World Cancer Research Fund/American Institute for Cancer Research monograph; for others, such as physical activity, obesity, and fruit and vegetable consumption, there have been more recent comprehensive reviews.3,11,12 In weighing the evidence from randomized controlled trials (RCTs), the Committee considered the findings in relation to the design of the trial, the specific question being addressed, and the importance of the trial results in the context of other evidence from human populations. Prospective cohort studies were weighted more heavily than case-control studies, especially when results were available from several cohorts. Population-based case-control studies with at least 200 cases of cancer were considered more informative than smaller or hospital-based case-control studies. Studies that adjusted for total energy intake, considered other dietary factors, and controlled for other known risk factors were considered more credible than those that failed to meet these criteria.
For many issues concerning nutrition and cancer, the evidence is not definitive, either because the published results are inconsistent, and/or because the methods of studying nutrition and chronic disease in human populations are still in evolution. Part of the uncertainty has resulted from studies that focus on specific nutrients or foods in isolation, thereby oversimplifying the complexity of foods and dietary patterns; the importance of dose, timing, and duration of exposure; and the large variations in nutritional status among human populations. Nutritional research is equally challenging in RCTs, generally considered the gold standard for scientific conclusions. Studies may fail to find an effect if the intervention begins too late in life, is too small, or if the follow up is too short for a benefit to appear. No single trial can resolve all of the questions that are relevant to the potential effects of nutrition throughout the lifespan. Moreover, many important questions about how diet, physical activity, and obesity relate to cancer cannot presently be addressed in RCTs. For example, randomized trials of weight loss in relation to cancer risk are severely constrained by the current lack of effective behavioral or pharmacologic approaches to help people lose weight and sustain a healthy weight. The cost and difficulty of randomized trials to determine the long-term consequences of interventions that begin in infancy and extend for many years preclude long-term experimental interventions. Interventions are ethical only if they can plausibly improve the health of the participants. Although it might be easier to motivate people to increase their weight by consuming more calories and/or fat and by decreasing their physical activity, such studies are clearly unethical.
Inferences about the many complex interrelationships among body weight, physical activity, diet, and cancer risk are therefore based, for the most part, on a combination of clinical trials and observational studies coupled with advancing understanding of the biology of cancer. These Guidelines are based on the totality of evidence from all sources, taking into account both the potential health benefits and possible risks from the intervention. No diet or lifestyle pattern can guarantee full protection against any disease; the potential health benefit represents a decreased likelihood that the disease will occur, not a guarantee of total protection. These Guidelines provide a concise and understandable summary of the existing scientific information about weight control, physical activity, and nutrition in relation to cancer. The ACS Guidelines are consistent with guidelines established for cancer prevention by other countries8; those from the American Heart Association and American Diabetes Association for the prevention of coronary heart disease and diabetes13,14; as well as for general health promotion, as defined by the 2005 Dietary Guidelines for Americans.15
In addition to recommendations regarding individual choices related to weight control, physical activity, and diet, the ACS Guidelines underscore what communities can and should do to facilitate healthy eating and physical activity behaviors (Table 1). Community efforts are essential to create a social environment that promotes healthy food choices and physical activity. Thus, the recommendation for community action recognizes that a supportive social environment is indispensable if individuals at all levels of society are to have genuine opportunities to choose healthy behaviors.
Table TABLE 1. American Cancer Society (ACS) Guidelines on Nutrition and Physical Activity for Cancer Prevention
|Maintain a healthy weight throughout life. |
• Balance caloric intake with physical activity.
• Avoid excessive weight gain throughout the life cycle.
• Achieve and maintain a healthy weight if currently overweight or obese.
|Adopt a physically active lifestyle. |
• Adults: engage in at least 30 minutes of moderate to vigorous physical activity, above usual activities, on 5 or more days of the week. Forty-five to 60 minutes of intentional physical activity are preferable.
• Children and adolescents: engage in at least 60 minutes per day of moderate to vigorous physical activity at least 5 days per week.
|Consume a healthy diet, with an emphasis on plant sources. |
• Choose foods and beverages in amounts that help achieve and maintain a healthy weight.
• Eat five or more servings of a variety of vegetables and fruits each day.
• Choose whole grains in preference to processed (refined) grains.
• Limit consumption of processed and red meats.
|If you drink alcoholic beverages, limit consumption. |
|ACS Recommendations for Community Action|
|Public, private, and community organizations should work to create social and physical environments that support the adoption and maintenance of healthful nutrition and physical activity behaviors. |
• Increase access to healthful foods in schools, worksites, and communities.
• Provide safe, enjoyable, and accessible environments for physical activity in schools, and for transportation and recreation in communities.
AMERICAN CANCER SOCIETY GUIDELINES FOR NUTRITION AND PHYSICAL ACTIVITY
Recommendations for Community Action
Social, economic, and cultural factors strongly influence individual choices about diet and physical activity. Although many Americans would like to adopt a healthy lifestyle, many encounter substantial barriers that make it difficult to follow diet and activity guidelines. Indeed, current trends toward increasing portion sizes,16, , –19 as well as the consumption of high-calorie convenience foods, beverages, and restaurant meals, and declining levels of physical activity are contributing to an obesity epidemic among Americans of all ages and across all population segments.15,20,21 Longer workdays and more households with multiple wage earners reduce the amount of time available for preparation of meals, with a resulting shift toward increased consumption of high-calorie food outside the home—frequently less nutritious than foods prepared at home.22 Large portion sizes and calorie-dense foods are used extensively in marketing by restaurants, supermarkets, and food companies.16, , –19 Reduced leisure time, increased reliance on automobiles for transportation, and increased availability of electronic entertainment and communications media all contribute to reduced physical activity.20,21 Increasing evidence indicates associations between the built environment and obesity and physical activity levels.23,24 Poor access to sidewalks, parks, and recreation facilities is associated with greater obesity risk,25 whereas neighborhoods that facilitate walking and safe physical recreation have lower obesity prevalence.23
The increase in obesity and physical inactivity is of particular concern for a number of population groups, including children, who are establishing lifetime behavioral patterns that affect health, and lower-income populations, who face additional problems because nearby stores often lack affordable and attractive healthy foods, and safety concerns limit opportunities for physical activity.
Facilitating improved diet and increased physical activity patterns in communities will require multiple strategies and bold action, ranging from the implementation of community, worksite, and other health promotion programs to policies that affect community planning, transportation, school-based physical education, and food services. Particular efforts will be needed to ensure that all population groups have access to healthy food choices and opportunities for physical activity. Public and private organizations at local, state, and national levels will need to develop new policies and to reallocate or expand resources to facilitate necessary changes. Health care professionals and community leaders, in particular, have new opportunities to provide leadership and to promote policy changes in their communities.
Lessons learned from the tobacco epidemic exemplify the power of social context in changing health behaviors. Adult per-capita cigarette consumption increased steeply from 1910 until 1964, when the first US Surgeon General Report publicized the health hazards of smoking. However, public education alone produced only a gradual decrease in cigarette consumption from 1964 through the early 1980s. It was the subsequent introduction of community-wide policy approaches that produced much larger reductions in cigarette smoking among children and adults, beginning in the mid-1980s. These included restrictions on cigarette advertising, increases in the price of tobacco products through taxation, laws preventing exposure to secondhand smoke in public places, and restrictions on the access of children to tobacco products. Only recently have communities begun to consider policy approaches that might promote better nutrition and physical activity at the population level. Public, private, and community organizations are now considering policy measures and strategies that could help individuals choose healthier patterns of nutrition and physical activity (Table 1).
Recommendations for Individual Choices
Approximately two-thirds of Americans are overweight or obese. The percentage of children, adolescents, and adult men who are overweight or obese has continued to increase through 2004, although the trend has now stabilized in adult women.26 In addition, many Americans are less physically active than is optimal for health. There is no longer serious medical debate about whether obesity, the prevalence of which has doubled in the last 25 years, constitutes a major health problem in the United States, increasing the risk of several cancers as well as of coronary heart disease, type 2 diabetes, and other medical problems. For most people in the United States, weight gain results from a combination of excessive caloric intake and inadequate physical activity. Thus, while there continues to be genuine scientific uncertainty about how specific aspects of excess adiposity, excessive energy intake, and physical inactivity relate to cancer, there is no debate about whether these constitute a serious and growing health problem. These Guidelines therefore emphasize the importance of maintaining a healthy body weight, adopting a physically active lifestyle, and consuming a healthy diet, particularly within the context of weight management.
1. Maintain a Healthy Weight Throughout Life
• Balance caloric intake with physical activity.
• Avoid excessive weight gain throughout the life cycle.
• Achieve and maintain a healthy weight if currently overweight or obese.
Body Weight and Cancer Risk
In the United States, overweight and obesity contribute to 14% to 20% of all cancer-related mortality.27 Overweight and obesity are clearly associated with increased risk for developing many cancers, including cancers of the breast in postmenopausal women,3,27, , , , , –33 colon, endometrium, adenocarcinoma of the esophagus, and kidney. Evidence is highly suggestive that obesity also increases risk for cancers of the pancreas, gallbladder, thyroid, ovary, and cervix, and for multiple myeloma, Hodgkin lymphoma, and aggressive prostate cancer.3,27, , , , , –33 These findings are supported by both epidemiologic studies in humans and other research.3,27, , , , , –33 Overweight and obesity are thought to affect risk of these cancers through a variety of mechanisms, some of which are specific to particular cancer types. These mechanisms include effects on fat and sugar metabolism; immune function; levels of several hormones, including insulin and estradiol; factors that regulate cell proliferation and growth, such as insulin-like growth factor-1; and proteins that make hormones more or less available to tissues, such as sex hormone-binding globulin.3 Overweight and obesity may increase risk of adenocarcinoma of the esophagus by increasing risk of gastroesophageal reflux disease and Barrett's esophagus.3
Most research on energy imbalance and cancer focuses on increased risks associated with overweight and obesity. Recently, studies exploring intentional weight loss suggest that losing weight may reduce the risk of breast cancer.34, , , –38 Surgery to treat morbid obesity and short-term intentional weight loss have been shown to improve insulin sensitivity and biochemical measures of hormone metabolism, which have been postulated to contribute to the relationship between obesity and certain cancers. The surgical removal of intra-abdominal fat has also been shown to reduce the metabolic syndrome. Even though our knowledge about the relationship between weight loss and cancer risk is incomplete, individuals who are overweight or obese should be encouraged and supported in their efforts to reduce weight.
Achieving and Maintaining a Healthy Weight
A healthy weight depends on a person's height, so recommendations for a healthy weight are often expressed in terms of a body mass index (BMI) (Table 2). BMI is calculated as body weight in kilograms divided by height in meters, squared.2 Exact cutoffs for a healthy weight are somewhat arbitrary, but for most Americans, experts consider a BMI within the range of 18.5 to 25.0 kg/m2 to be healthy, a BMI between 25.0 and 29.9 to be overweight, and a BMI of 30.0 and over to be obese. Individuals should strive to maintain healthy weights as illustrated in Table 2.
Table TABLE 2. Adult BMI Chart
|Height||Weight in Pounds|
| ||Healthy Weight||Overweight||Obese|
The way to achieve a healthy body weight is to balance energy intake (food and beverage intake) with energy expenditure (physical activity).3,15 Excess body fat can be reduced by reducing caloric intake and increasing physical activity. For most adults a reduction of 50 to 100 calories per day may prevent gradual weight gain, whereas a reduction of 500 calories or more per day is a common initial goal in weight loss programs. Similarly, up to 60 minutes of moderate to vigorous intensity physical activity per day may be needed to prevent weight gain, but as much as 60 to 90 minutes of moderate intensity physical activity per day may help to sustain weight loss for previously overweight people.15 The healthiest way to reduce caloric intake is to reduce intake of added sugars, saturated and trans fats, and alcohol, which all provide substantial calories, but few or no essential nutrients. Caloric intake can be reduced by decreasing the size of food portions (see standard serving sizes [Table 3]) and limiting the intake of foods and beverages that are high in calories, fat, and/or refined sugars, and which provide few nutrients (eg, fried foods, cookies, cakes, candy, ice cream, and soft drinks). Such foods and beverages should be replaced with choices like vegetables and fruits, whole grains, beans, and lower-calorie beverages.39 People should be aware that meals served in fast-food establishments and restaurants typically exceed the portion sizes needed to meet recommended daily caloric intake and are often high in hidden fats.39 They also are often low in vegetables, fruits, whole grains, and beans.22 Monitoring food intake and physical activity has been shown to be effective in weight management.19,39,40
Table TABLE 3. What Counts as a Serving
• 1 medium apple, banana, orange
• 1/2 cup of chopped, cooked, orcanned fruit
• 1/2 cup of 100% fruit juice
• 1 cup of raw leafy vegetables
• 1/2 cup of other cooked or raw vegetables, chopped
• 1/2 cup of 100% vegetable juice
• 1 slice bread
• 1 ounce ready-to-eat cereal
• 1/2 cup of cooked cereal, rice, pasta
|Beans and nuts|
|Dairy foods and eggs|
|Meats||2–3 ounces of cooked lean meat, poultry, fish|
The health of young people, and the adults they will become, is critically linked to the establishment of healthy behaviors in childhood.41 Risk factors such as excess weight gain, unhealthy dietary patterns, and physical inactivity during childhood and adolescence can result in increased risk of developing cancer, cardiovascular disease, diabetes, hypertension, and osteoporosis later in life.41 Children who adopt healthy lifestyle habits at an early age are more likely to continue these behaviors throughout life. About half of youngsters who are overweight as children will remain overweight in adulthood42; 70% of those who are overweight by adolescence will remain overweight as adults.18 For these reasons, efforts to establish healthy weight and patterns of weight gain should begin in childhood.
2. Adopt a Physically Active Lifestyle
• Adults: engage in at least 30 minutes of moderate to vigorous physical activity, above usual activities, on 5 or more days of the week. Forty-five to 60 minutes of intentional physical activity are preferable.
• Children and adolescents: engage in at least 60 minutes per day of moderate to vigorous physical activity at least 5 days per week.
Benefits of Physical Activity
Scientific evidence indicates that physical activity may reduce the risk of several types of cancer, including cancers of the breast, colon, prostate, and endometrium.3,29,43 Although scientific evidence for many other cancers is lacking, associations may exist. Physical activity acts in a variety of ways to impact cancer risk.44 Regular and intentional physical activity helps maintain a healthy body weight by balancing caloric intake with energy expenditure.45 Other mechanisms by which physical activity may help to prevent certain cancers may involve both direct and indirect effects, including regulating sex hormones, insulin, prostaglandins, and various beneficial effects on the immune system.3,46,47 The benefits of a physically active lifestyle far exceed reducing the risk of cancer and provide other important health benefits,3 including associations with reduced risk of other chronic diseases, such as heart disease, diabetes, osteoporosis, and hypertension.48
Types of Activity
Usual activities are those that are performed on a regular basis as part of one's daily routine. These activities include those performed at work (such as walking from the parking garage to the office), at home (such as climbing a flight of stairs), as well as those considered activities of daily living (such as dressing and bathing). They are typically of low intensity and short duration. Intentional activities are those that are done in addition to these usual activities. These activities are often planned and often done at leisure, for exercise, for fitness, or transportation to intentionally supplement other routine activities. These activities range from a bike ride or a run to including more purposeful physical activity into the day, such as walking to use public transportation instead of driving. Moderate activities are those that require effort equivalent to a brisk walk.49 Vigorous activities generally engage large muscle groups and cause a noticeable increase in heart rate, breathing depth and frequency, and sweating. 49 These activities can be performed in a variety of settings: occupational, recreational, in the home or garden, and with friends or family.49
Recommended Amount of Totaland Intentional Activity
Although the optimal intensity, duration, and frequency of physical activity needed to reduce cancer risk are unknown, evidence suggests that at least 30 minutes of moderate to vigorous activity, in addition to usual activities done throughout the day, can help reduce cancer risk. Evidence is accumulating that 45 to 60 minutes on 5 or more days of the week may be optimal to reduce risk of cancers of the colon and breast.3 There is limited evidence regarding whether physical activity is most protective if done in a single session or in increments throughout the day, but it is reasonable to assume that benefit can be accumulated in separate sessions of 20 to 30 minutes each.
Data suggest that 60 minutes of moderate to vigorous activity on 5 or more days per week helps to prevent weight gain and obesity.15,50 By helping to maintain weight, physical activity for 60 minutes on 5 or more days of the week may have an indirect effect on reducing the risk of developing obesity-related cancers.51, , , –55 Apart from effects on obesity, physical activity appears to have other effects on reducing the risk of cancers of the colon and breast, even when activity is not initiated until later in life.55
For people who are largely inactive or just beginning a physical activity program, a gradual increase to 30 minutes per day of moderate intensity physical activity on at least 5 days per week will provide substantial cardiovascular benefits.56,57 After this duration is achieved, increasing intensity to vigorous levels may further improve health benefits for those individuals who are able to exercise at this intensity. Most children and young adults can safely engage in moderate physical activity without consulting their physicians. However, men older than 40 years, women older than 50 years, and people with chronic illnesses and/or established cardiovascular risk factors should consult their physicians before beginning a vigorous physical activity program. Stretching and warm-up periods before and after activity can reduce the risk of musculoskeletal injuries and muscle soreness.
Individuals who are already active at least 30 minutes on most days of the week should strive to accumulate 60 minutes of moderate or greater intensity activity on most days of the week. Selected examples of moderate and vigorous activities are provided in Table 4.
Table TABLE 4. Examples of Moderate and Vigorous Intensity Physical Activities
|Exercise and leisure||Walking, dancing, leisurely bicycling, ice and roller skating, horseback riding, canoeing, yoga||Jogging or running, fast bicycling, circuit weight training, aerobic dance, martial arts, jumping rope, swimming|
|Sports||Volleyball, golfing, softball, baseball, badminton, doubles tennis, downhill skiing||Soccer, field or ice hockey, lacrosse, singles tennis, racquetball, basketball, cross-country skiing|
|Home activities||Mowing the lawn, general yard and garden maintenance||Digging, carrying and hauling, masonry, carpentry|
|Occupational activity||Walking and lifting as part of the job (custodial work, farming, auto or machine repair)||Heavy manual labor (forestry, construction, firefighting)|
Adopting a physically active lifestyle involves making deliberate decisions and changing lifestyle behaviors to select active rather than sedentary behavior. To enhance the ability of individuals to adopt a more active lifestyle, both communities and individuals need to implement changes (see Recommendation for Community Action). Ideas to reduce sedentary behavior are suggested in Table 5.
Table TABLE 5. Suggested Ways to Reduce Sedentary Behavior
• Use stairs rather than an elevator.
• If you can, walk or bike to your destination.
• Exercise at lunch with your coworkers, family, or friends.
• Take an exercise break at work to stretch or take a quick walk.
• Walk to visit coworkers instead of sending an e-mail.
• Go dancing with your spouse or friends.
• Plan active vacations rather than only driving trips.
• Wear a pedometer every day and increase your daily steps.
• Join a sports team.
• Use a stationary bicycle or treadmill while watching TV.
• Plan your exercise routine to gradually increase the days per week and minutes per session.
• Spend time playing with your kids.
Physical activity plays an important role in children's and adolescents' health and well-being and has important physical, mental, and social benefits.15,58,59 Because one of the best predictors of adult physical activity is activity level during childhood and adolescence, and because physical activity plays a critical role in weight maintenance, children and adolescents should be encouraged to be physically active at moderateto vigorous intensities for at least 60 minutes per day on 5 or more days per week.60,61 Activities should be developmentally appropriate, enjoyable, and varied,59 including sports and fitness activities in school, at home, and in the community.62 Because children and adolescents spend a significant portion of their days in schools, the availability of routine, high-quality physical education programs is a critically important and recognized way of increasing physical activity among youth.62 To help achieve activity goals, daily physical education programs and activity breaks should be provided for children at school, and television viewing and computer game time should be minimized at home.
Although the health benefits of physical activity in preventing cancer and other chronic diseases are facilitated by the development of healthy activity patterns in childhood, benefit seems to accumulate over the course of a lifetime.6 Therefore, increasing the level of physical activity at any age can provide important health benefits and may reduce the risk of some cancers.
3. Consume a Healthy Diet, with an Emphasison Plant Sources
Choose foods and beverages in amounts that help achieve and maintain a healthy weight.
• Become familiar with standard serving sizes, and read food labels to become more aware of actual servings consumed.
• Eat smaller portions of high-calorie foods. Be aware that “low-fat” or “nonfat” does not mean “low-calorie,” and that low-fat cakes, cookies, and similar foods are often high in calories.
• Substitute vegetables, fruits, and other low-calorie foods and beverages for calorie-dense foods and beverages such as French fries, cheeseburgers, pizza, ice cream, doughnuts and other sweets, and regular sodas.
• When you eat away from home, choose food low in calories, fat, and sugar, and avoid large portion sizes.
Eat five or more servings of vegetables and fruits each day.
• Include vegetables and fruits at every meal and for snacks.
• Eat a variety of vegetables and fruits each day.
• Limit French fries, chips, and other fried vegetable products.
• Choose 100% juice if you drink vegetable or fruit juices.
Choose whole grains in preferences to processed (refined) grains and sugars.
• Choose whole grain rice, bread, pasta, and cereals.
• Limit consumption of refined carbohydrates, including pastries, sweetened cereals, and other high-sugar foods.
Limit consumption of processed and red meats.
• Choose fish, poultry, or beans as an alternative to beef, pork, and lamb.
• When you eat meat, select lean cuts and eat smaller portions.
• Prepare meat by baking, broiling, or poaching rather than by frying or charbroiling.
The scientific study of nutrition and cancer is highly complex, and many important questions remain unanswered. For example, it is not presently completely understood how energy imbalance or how single or combined nutrients or foods affect one's risk of specific cancers. In addition, many dietary factors and lifestyle practices tend to correlate with each other; for example, people who consume a diet high in vegetables and fruits also tend to eat less meat and be more physically active.63 Foods and nutrients may have additive or synergistic effects on health and need to be considered in the context of the total diet. Studies have shown that individuals whose diets are very low in vegetables and fruits and whole grains, and high in processed and red meats, tend to have an increased risk of some of the most common types of cancers.64,65 Until more is known about the specific components of diet that influence cancer risk, the best advice is to consume whole foods following an overall healthy dietary pattern as outlined, with special emphasis placed on controlling total caloric intake to help achieve and maintain a healthy weight.
Choosing Foods and Beverages in Amounts That Achieve and Maintain a Healthy Weight
Most people cannot maintain a healthy weight without limiting caloric intake while maintaining regular physical activity. Unfortunately, current trends indicate that the largest percentage of calories in the American diet comes from foods high in fat, sugar, and refined carbohydrates.66 Consuming a varied diet that emphasizes plant foods may help to displace these calorie-dense foods. Limiting portion sizes, especially of these types of foods, is another important strategy to reduce total caloric intake.
Replacing dietary fat with foods that are high in calories from added sugar and other refined carbohydrates does not protect against overweight or obesity. The decrease in fat intake and increase in refined carbohydrates that occurred in the United States between 1977 and 1995 coincided with an 8% increase in the prevalence of obesity.67,68 Many processed foods, including soft drinks and fruit drinks, presweetened cereals, pastries, candies, and syrups, contain large amounts of added sugars. These added sugars come in many forms, such as glucose, high-fructose corn syrup, fruit juice concentrates, and honey. Consuming products high in these added sugars adds little nutrient value to the diet, contributes to excess energy intake, and may contribute to insulin resistance, alterations in the amount and distribution of body fat, and increased concentrations of growth factors that may promote the growth of cancers.
Vegetables and Fruits
Vegetables (including legumes) and fruits are complex foods, each containing numerous potentially beneficial vitamins, minerals, fiber, carotenoids, and other bioactive substances, such as flavonoids, terpenes, sterols, indoles, and phenols that may help prevent cancer.11 Greater consumption of vegetables and fruits is associated with decreased risk of lung, esophageal, stomach, and colorectal cancer.11 For other cancers, evidence is either limited or inconsistent, although the role of vegetables and fruits may indirectly influence cancer risk via their effects on energy intake. Intervention studies of dietary patterns, including high consumption of vegetables and fruits, have not been associated with a reduced risk of developing adenomatous polyps69 or colon cancer,70 but the degree of adherence to and achievement of study goals over several years among free-living individuals may limit interpretability. Although the strength of the cumulative evidence that total intake of vegetables and/or fruits decreases cancer risk has weakened in recent years, the totality of the evidence remains strong for a risk reduction associated with vegetable and fruit consumption at a variety of cancer sites.11 There is ongoing research on the potential benefits of particular vegetables and fruits, or groups of these, including dark green and orange vegetables, cruciferous vegetables (eg, cabbage, broccoli, cauliflower, Brussels sprouts), soy products, legumes, Allium vegetables (onions and garlic), and tomato products.
In addition to providing nutrients that may be beneficial in reducing cancer risk, vegetables and fruits may also contribute to weight maintenance, although the epidemiologic evidence supporting such an association is limited.71 Some evidence suggests that individuals who eat more vegetables and fruits have less weight gain and lower risk of developing obesity over time.72 Intake of vegetables and fruits may be particularly important if their consumption replaces other, more calorically dense foods as a strategy for maintaining a healthy weight. For that reason, consumption of low-calorie, whole vegetables and fruits should be encouraged. Consumption of vegetables and fruits that are fried (eg, French fries) or consumed with calorically dense sauces (eg, broccoli with cheese sauce), or high-calorie fruit juices and/or drinks does not help achieve this objective.
Evidence that vegetable and fruit consumption reduces cancer risk has led to attempts to isolate specific nutrients and administer them as supplements, sometimes in very high doses.73 Most of these attempts have been unsuccessful in preventing cancer or its precursor lesions, and in some cases, have had adverse effects.73 Some of this may be due to the methodologic challenges of studying nutrients in RCTs for cancer; investigators must often select exact doses, duration, and timing of a single nutrient intervention, based on evidence derived from broader observational data on whole foods, like vegetables and fruits. Notable examples are the four randomized trials of beta carotene for the prevention of lung cancer, which were initiated because many observational epidemiologic studies had indicated a lower risk of lung cancer in persons eating foods high in beta carotene.74,75 In two of these trials, the individuals taking high-dose beta carotene supplements developed lung cancer at higher rates than those taking a placebo.76, –78 Although there has been considerable evidence from observational studies that people consuming more beta carotene from foods were at reduced risk for lung cancer, these findings support the idea that beta carotene may be only a proxy for other single nutrients or combinations of nutrients found in whole foods, and that taking a single nutrient in large amounts can be harmful, at least for some subgroups of the population.
A number of different recommendations have been made to encourage Americans to increase the number of servings of vegetables and fruits they consume.13,15,79 Despite these recommendations, intake of these foods remains low among adults and children.80,81 This may be due to several reasons, including lack of access to affordable produce, preparation time, and taste preferences.82, , –85
Eating a diet rich in vegetables and fruitsmay reduce cancer risk both directly and indirectly by contributing to maintenance of a healthy weight.11,71 Vegetable and fruit consumption has also been found to be associated with reduced risk of other chronic diseases, particularly cardiovascular disease, an important contributor to overall morbidity and mortality in the United States.13,86, –88 For cancer risk reduction, the recommendation is to consume at least five servings of a variety of vegetables and fruits each day; however, for overall health, the ACS supports the recommendation to consume higher levels, depending on calorie needs, as stated in the US Department of Health and Human Services' Dietary Guidelines for Americans.15
Grains such as wheat, rice, oats, and barley, and the foods made from them, are an important part of an overall healthful diet. Whole grain foods, which are those made from the entire grain seed, are relatively low in caloric density and can contribute to maintaining energy balance.15,89 In addition, whole grains are higher in fiber, certain vitamins, and minerals than processed (refined) flour products. Some of these vitamins and minerals have been associated with lower risk of cancer.90 The association between whole grain foods and different types of cancer has been inconsistent, however, possibly because the questionnaires used in these studies to assess dietary intake were generally not specifically designed to assess whole grain consumption, which in most cases resulted in incomplete assessments.
Consumption of high-fiber foods is associated with a lower risk of several chronic diseases, including diabetes, cardiovascular disease, and diverticulitis.15 Consuming high-fiber foods, such as legumes and whole grain breads, cereals, rice, and pasta, is therefore highly recommended, even though data for an association between fiber and cancer risk are limited.69,91,92 Because the benefits of whole grain foods may derive from their other nutrients as well as fiber, it is preferable to consume whole grain foods rather than fiber supplements.
Processed and Red Meats
Many epidemiologic studies have examined the association between cancer and the consumption of red meats (defined as beef, pork, or lamb) and processed meats (cold cuts, bacon, hot dogs, etc.). Current evidence supports an increased risk of cancers of the colon and/or rectum93, , –96 and prostate.97,98 More limited evidence exists for other sites. Studies that have examined red meat and processed meat separately suggest that risks associated with processed meat may be slightly greater than red meat,93, –95,98 but the consumption of both should be limited.
Meat contains several constituents that could increase the risk of cancer.97,99 Mutagens and carcinogens (heterocyclic amines and polycyclic aromatic hydrocarbons) are produced by cooking meat at high temperatures and/or by charcoal grilling. The iron content (heme) in red meat may generate free radicals in the colon that damage DNA. Substances used to process meat (nitrates/nitrites and salt) contribute to theformation of nitrosamines that can damage DNA. It is also possible that the fat content in meat contributes to risk. For example, foods that are high in fat increase the concentration of secondary bile acids and other compounds in the stool that could be carcinogens or promoters of carcinogenesis.
Although meats are good sources of high-quality protein and can supply many important vitamins and minerals, they remain major contributors of total fat, saturated fat, and cholesterol in the American diet.100 The recommendation is to limit consumption of processed and red meats. To accomplish this, choose lean meats and smaller portions, and use meat as a side dish rather than as the focus of a meal. Legumes are especially rich in nutrients that may protect against cancer and can be a healthier source of protein than red meats. Although cooking meat at high temperatures, such as in grilling or frying, can produce potential carcinogens, care should be taken to cook meat thoroughly to destroy harmful bacteria and parasites, but to avoid charring.
4. If You Drink Alcoholic Beverages, Limit Consumption
People who drink alcohol should limit their intake to no more than two drinks per day for men and one drink a day for women.15 The recommended limit is lower for women because of their smaller body size and slower metabolism of alcohol. A drink of alcohol is defined as 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of80-proof distilled spirits. Alcohol consumption is an established cause of cancers of the mouth, pharynx, larynx, esophagus, and liver.5,101 For each of these cancers, risk increases substantially with intake of more than two drinks per day.5,101 Alcohol consumption combined with tobacco increases the risk of cancers of the mouth, larynx, and esophagus far more than the independent effect of either drinking or smoking.5 Extensive evidence also implicates alcohol consumption as a cause of cancer of the breast,102, –104 and probably colon and rectum cancer.5,105 Regular consumption of more than one drink per day has been associated with an increased risk of breast cancer in women.103 The mechanism by which alcohol is related to breast cancer is not known, but it may be due to alcohol-induced increases in circulating estrogens or other hormones in the blood, reduction of folate levels, or to a direct effect of alcohol or its metabolites on breast tissue. Reducing alcohol consumption may be an important way for many women to reduce their risk of breast cancer. In particular, women with a low intake of folate may be more susceptible to the increase in breast cancer risk from alcohol.106, , –109 Overall, the evidence seems to indicate that total alcohol consumption is the important factor, not the type of alcoholic beverage consumed.110
Complicating the recommendation for alcohol and cancer risk reduction is the fact that low to moderate intake of alcoholic beverages has been associated with decreased risk of coronary heart disease.102 Even though drinking moderate levels of alcohol is associated with reduced risk of coronary heart disease in women, those women who are at high risk of breast cancer might reasonably consider abstaining from alcohol. There is no compelling reason for adults who currently do not consume alcoholic beverages to start consuming alcohol to reduce their risk for heart disease, as cardiovascular risk can be reduced by other means, such as avoiding smoking, consuming a diet low in saturated and trans fats, maintaining a healthy weight, staying physically active on a regular basis, and controlling blood pressure and lipids. Furthermore, there is convincing evidence that cardiovascular risk increases with heavy alcohol consumption.102 Some groups of people should not drink alcoholic beverages at all. These include children and adolescents; individuals of any age who cannot restrict their drinking to moderate levels or who have a family history of alcoholism; women who are or may become pregnant; individuals who plan to drive or operate machinery or who take part in other activities that require attention, skill, or coordination; and individuals taking prescriptions or over-the-counter medications that can interact with alcohol.
DIET AND PHYSICAL ACTIVITY FACTORS THAT AFFECT RISKS FOR SELECT CANCERS
The major risk factors for bladder cancer are tobacco smoking and exposure to certain industrial chemicals. Limited evidence suggests that drinking more fluids may lower the risk of bladder cancer, as may eating more vegetables.111
There are no known nutritional risk factors for brain tumors at this time.
Breast cancer is the most common cancer diagnosed among American women and is second only to lung cancer as a cause of cancer deaths in women.134 The risk of breast cancer is increased by several reproductive and other factors that are not easily modified: menarche before age 12, nulliparity or first birth at age greater than 30 years, late age at menopause, and a family history of breast cancer. Risk factors may differ for breast cancer that is diagnosed before or after menopause. New evidence indicates that exposures throughout life including in utero may have an effect on breast cancer risk. That breast cancer risk is increased with increasing adult height strongly points to early-life nutritional factors in breast cancer.
There is consistent evidence that increased body weight and weight gain during adulthood are associated with increased risk for breast cancer among postmenopausal (but not premenopausal) women.34,37,112, , , , –117 This increased risk is likely due to the higher levels of estrogens produced by extra adipose tissue after menopause; the adverse effect of weight gain is not seen as readily among women taking postmenopausal hormone therapy (hormone replacement therapy), since it may be masked by higher levels of exogenous estrogens. Alcohol intake is also associated with an increase in risk,103,104,118 particularly for women whose intake of folate is low.106, , –109 Moderate to vigorous physical activity has been shown to be associated with decreased breast cancer risk among both premenopausal and postmenopausal women.3 Although reduction of fat intake to very low levels may reduce breast cancer risk, results from the recent intervention trial found that lowering fat intake to 29% of calories had only a very small effect on risk among postmenopausal women.119 At the present time, the best nutritional advice to reduce the risk of breast cancer is to engage in moderate to vigorous physical activity 45 to 60 minutes on 5 or more days per week, minimize lifetime weight gain through the combination of caloric restriction and regular physical activity, and avoid or limit intake of alcoholic beverages.6,104,115,120,121
Colorectal cancer is the second leading cause of cancer death among American men and women combined.134 The risk of colorectal cancer is increased in those with a family history of colorectal cancer. Long-term tobacco use and possibly excessive alcohol consumption increase risk, whereas use of aspirin or other nonsteroidal anti-inflammatory drugs, postmenopausal hormone therapy, and possibly increased calcium intake may decrease risk. Currently, however, neither aspirin-like drugs nor postmenopausal hormones are recommended to prevent colorectal cancer because of their potential adverse effects. Studies demonstrate a lower risk of colon cancer among those who are moderately active on a regular basis, and increasing evidence suggests that more vigorous activity may have an even greater benefit in reducing the risk of colon cancer.53,122 Obesity increases the risk of colon cancer among both men and women, but the association seems to be stronger in men.3,27 Diets high in vegetables and fruits have been associated with decreased risk,11 and diets high in processed and/or red meat have been associated with increased risk of colon cancer.123, –125 A growing number of studies support a protective role of calcium126,127 for colorectal cancer or its precursor, colorectal adenomas. Several studies also suggest that vitamin D128,129 or a combination of vitamin D and calcium130 may prevent this cancer. However, because of a potential increase in risk of prostate cancer associated with calcium intake,131 it would be prudent to limit calcium intake in men to less than 1,500 mg/day until further studies are conducted. The best nutritional advice to reduce the risk of colon cancer is to increase the intensity and duration of physical activity; limit intake of red and processed meat; consume recommended levels of calcium; eat more vegetables and fruits; avoid obesity; and avoid excess alcohol consumption (eg, no more than one drink/day in women, two drinks/day in men).53,54,122,132 In addition, it is very important to follow the ACS guidelines for regular colorectal screening, as identifying and removing precursor polyps in the colon can prevent colorectal cancer.133
Endometrial cancer is the most common female reproductive cancer in the United States, ranking fourth among all cancers in women in age-adjusted incidence.134 Although endometrial cancer has been traditionally considered as a single entity, epidemiologic and clinicopathologic evidence points to two separate types. Type I endometrial cancer (low grade, the most common type) is hormonally related, associated with hyperplasia, and tends to have a better prognosis. Type II endometrial cancer (high grade, approximately 10% of endometrial cancers) is not hormonally related, is associated with endometrial atrophy, and tends to have a worse prognosis.135 Most of the established risk factors for endometrial cancer, summarized here, refer to type I; the causes of type II endometrial are largely unknown.
Most of the major known risk factors for type I endometrial cancer have in common a prolonged and excessive exposure of the endometrium to estrogens unopposed by progesterone, such as postmenopausal estrogen therapy, sequential oral contraceptive formulations, a history of polycystic ovarian syndrome, and obesity.
There is strong evidence of a relationship between obesity and endometrial cancer.3 In premenopausal women, the increased risk has been attributed to insulin resistance, elevation in ovarian androgens, anovulation, and chronic progesterone deficiency associated with overweight.135 In postmenopausal women, the increased risk has been attributed to the higher circulating concentration of bioavailable estrogens created from the conversion of androstenedione to estrone in adipose tissue.3 Studies examining physical activity, which has also been shown to affect endogenous hormone levels, have suggested a decrease in endometrial cancer risk for the highest level of physical activity.3
Vegetable and fiber intakes may decrease risk, whereas red meat, saturated fat, and animal fat may increase risk.136 At the present time, the best advice to reduce the risk of endometrial cancer is to maintain a healthy weight through diet and regular physical activity, and eat a predominantly plant-based diet rich in vegetables, whole grains, and beans.
In the United States, kidney cancer accounts for 3% of both incident and fatal cancers in men and 2% of cancer cases and deaths in women.134 The incidence of kidney cancer has been steadily rising by nearly 2% annually since 1975.137 Approximately 80% to 85% of kidney cancers are renal cell cancers. The etiology of renal cell cancer is largely unknown; however, the most established modifiable risk factors include obesity and tobacco smoking. In 2002, the International Agency for Research on Cancer concluded that there is sufficient evidence for excessive weight as a cause of renal cell cancer.3 Results for associations between dietary factors and renal cell cancer risk have been limited or inconsistent. At the present time, the best advice to reduce the risk of kidney cancer is to maintain a healthy weight and avoid tobacco use.
Leukemias and Lymphomas
There are no known nutritional risk factors for leukemias or lymphomas at this time.
Lung cancer is the leading cause of cancer death among Americans.11,134 More than 85% of lung cancers occur because of tobacco smoking, and 10% to 14% are attributed to radon exposure. Many studies have found that the risk of lung cancer is lower among smokers and nonsmokers who consume at least five servings of vegetables and fruits a day. A recent review found significantly lower risk of lung cancer with higher consumption of fruit.11 Although healthful eating may reduce the risk of lung cancer, the risks posed by tobacco remain substantial. Nutritional supplementation with high doses of beta carotene and/or vitamin A has increased (not decreased) lung cancer risk among smokers (see Beta Carotene).76,77 At the present time, the best advice to reduce the risk of lung cancer is to avoid tobacco use and environmental tobacco smoke and to avoid radon exposure. Eating at least five servings of vegetables and fruits every day is also advised.7,138
Cancer of the ovary is the second most common gynecologic cancer and the leading cause of death from gynecologic malignancies.134 Although the etiology of ovarian cancer is not well understood, hormonal, environmental, and genetic factors have been implicated. Family history of ovarian cancer is a risk factor, but fewer than 10% of ovarian cancers are hereditary.
At the present time there are no established nutritional risk factors for ovarian cancer. In the Pooling Project of Diet and Cancer Cohorts, a study combining the data from 12 cohort studies,139 there was no indication of an association of risk with total fruit, total vegetable, total fruit and vegetable, or any botanically defined subgroup, and in the European Investigation into Cancer and Nutrition (EPIC) study,140 a very large cohort study of women in Europe, total fruit, total vegetables, or total fruit and vegetables were unrelated to ovarian cancer risk. The association with milk/dairy products and galactose metabolism has been widely explored with inconsistent results.141,142 There was no indication of an association with milk/dairy product or calcium consumption in a recent study pooling data from 12 cohort studies,143 whereas there was some indication of a weak association with lactose intake at a level equivalent to three or more glasses of milk per day. The overall evidence seems to indicate that alcohol consumption at moderate levels may reduce the risk of ovarian cancer.110,144,145 The role of obesity and physical activity in ovarian cancer risk is unclear.3,5,146
Pancreatic cancer is the fourth leading cause of cancer death in the United States.134 Substantial evidence indicates that tobacco smoking, adult-onset diabetes, and impaired glucose tolerance increase the risk for pancreatic cancer.147 Some studies have also shown that obesity and physical inactivity (both factors strongly linked to abnormal glucose metabolism) and higher consumption of red and processed meat are associated with elevated pancreatic cancer risk, and that fruit and vegetable intake is associated with reduced risk,148 but none of these relationships is yet firmly established. At the present time, the best advice to reduce the risk of pancreatic cancer is to avoid tobacco use, maintain a healthful weight, remain physically active, and eat five or more servings of vegetables and fruits each day.
Prostate cancer is the most common cancer among American men.134 Although prostate cancer is related to male sex hormones, just how nutritional factors might influence risk remains uncertain.149 Several studies suggest that diets high in certain vegetables (including tomatoes/tomato products, cruciferous vegetables, soy, beans, or other legumes) or fish are associated with decreased risk. There is some evidence that food or supplements containing specific antioxidant nutrients, such as vitamin E, selenium, beta carotene, and lycopene, may reduce prostate cancer risk. Whether vitamin E and/or selenium reduce prostate cancer incidence is currently being tested in a large clinical trial. Most epidemiologic studies have not consistently distinguished between specific nutrients and the foods in which they occur. The biological plausibility that certain nutrients may affect prostate cancer risk has been strengthened by recent reports of gene-diet interactions for these nutrients and specific genes involved in antioxidant function and DNA repair.149 Some of the genotypes were fairly common in the predominantly Caucasian populations studied (eg, 25%), and men with the specific genotype who had higher versus lower levels of these circulating nutrients were greatly protected against prostate cancer.150 Several studies have observed that greater consumption of red meat or dairy products may be associated with increased risk of prostate cancer.97,98,151 There is also evidence that a high calcium intake, primarily through supplements, is associated with increased risk for more aggressive types of prostate cancer.131,152 Although obesity has been inconsistently related to prostate cancer development, recent data suggest that being overweight is associated with worse prognosis after diagnosis and treatment among men with prostate cancer.31,153 Evidence suggests that exercise, in particular vigorous exercise, may impart some benefit for prostate cancer.3 At the present time, the best advice to reduce the risk of prostate cancer is to eat five or more servings of a wide variety of vegetables and fruits each day, limit intake of red meats and dairy products, and maintain an active lifestyle and healthy weight.
Stomach cancer is the fourth most common cancer worldwide and the number two cause of death from cancer.134 This cancer, however, is relatively uncommon in the United States. Many studies have found that high intake of fresh fruits and vegetables is associated with reduced risk of stomach cancer, whereas high intake of salt-preserved foods is associated with increased risk.154,155 There is also convincing evidence that chronic stomach infection by the bacterium Helicobacter pylori increases the risk of stomach cancer.154,155 Although the overall incidence of stomach cancer continues to decrease in most parts of the world, the incidence of this cancer in the gastric cardia has increased recently in the United States and several European countries.156 The reasons for the increase are under active investigation but may be tied to increases in lower esophageal cancers caused by gastric reflux from abdominal obesity.156 At the present time, the best advice for reducing the risk of stomach cancer is to eat at least five servings of vegetables and fruits daily, reduce salt-preserved food consumption, and maintain a healthy weight.
Upper Aerodigestive Tract Cancers
In the United States, upper digestive tract cancers are significantly more common among men than women. Tobacco (including cigarettes, chewing tobacco, and snuff) and alcohol, alone, but especially when used together, increase the risk for cancers of the mouth, larynx, pharynx, and esophagus; these exposures contributesubstantially to the gender disparities for these cancers. Obesity increases the incidence of adenocarcinoma in the lower esophagus and at the junction of the esophagus and stomach, likely as a result of epithelial damage, metaplasia, and dysplasia associated with acid reflux. There is some evidence to suggest that consuming beverages and foods that are very hot in temperature may increase risk for oral and esophageal cancers, likely as a result of thermal damage to exposed tissue. Eating recommended amounts of vegetables and fruits probably reduces the risk of oral and esophageal cancers. At the present time, the best advice to reduce the risk of cancers of the upper digestive and respiratory tracts is to avoid all forms of tobacco, restrict alcohol consumption, avoid obesity, and eat at least five servings of a variety of vegetables and fruits each day.157, –159
COMMON QUESTIONS ABOUT DIET, PHYSICAL ACTIVITY, AND CANCER
Because people are interested in the relationship that specific foods, nutrients, or lifestyle factors have to specific cancers, research on health behaviors and cancer risk is often widely publicized. Health professionals who counsel patients should emphasize that no one study provides the last word on any subject, and that individual news reports may overemphasize what appear to be contradictory or conflicting results. In brief news stories, reporters cannot always put new research findings in their proper context. The best advice about diet and physical activity is that it is rarely, if ever, advisable to change diet or activity levels based on a single study or news report. The following questions and answers address common concerns about diet and physical activity in relation to cancer.
Does alcohol increase cancer risk? Yes. Alcohol increases the risk of cancers of the mouth, pharynx, larynx, esophagus, liver, colorectum, and breast.5,101 People who drink alcohol should limit their intake to no more than two drinks per day for men and one drink per day for women.15 A drink is defined as 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of 80-proofdistilled spirits. The combination of alcohol and tobacco increases the risk of some cancers far more than the independent effects of either drinking or smoking.5 Regular consumption of even a few drinks per week is associated with an increased risk of breast cancer in women—a risk that is particularly high in women who do not get enough folate.103,104,109 Women at high risk of breast cancer may consider abstaining from alcohol.
What are antioxidants, and what do they have to do with cancer? Along with a number of other defense systems, the body appears to use certain nutrients in vegetables and fruits to protect the body against damage to tissues that occurs constantly as a result of normal metabolism (oxidation). Because such damage is associated with increased cancer risk, the so-called antioxidant nutrients are thought to protect against cancer.160 Antioxidants include vitamin C, vitamin E, carotenoids, and many other phytochemicals. Studies suggest that people who eat more vegetables and fruits, which are rich sources of antioxidants, may have a lower risk for some types of cancer.11 Clinical studies of antioxidant supplements are currently under way, but studies have not yet demonstrated a reduction in cancer risk from vitamin or mineral supplements73 (see also Beta Carotene, Lycopene, Vitamin E, Supplements). To reduce cancer risk, the best advice presently is to consume antioxidants through food sources rather than supplements.
Does aspartame cause cancer? No. Aspartame is a low-calorie artificial sweetener that is about 200 times sweeter than sugar. Current evidence does not demonstrate any link between aspartame ingestion and increased cancer risk.161,162 People with the genetic disorder phenylketonuria should avoid aspartame in their diets.
Does beta carotene reduce cancer risk? Because beta carotene, an antioxidant chemically related to vitamin A, is found in vegetables and fruits, and because eating vegetables and fruits is associated with a reduced risk of cancer, it seemed plausible that taking high doses of beta carotene supplements might reduce cancer risk. However, the results of three major clinical trials show this is not the case. In two studies in which people were given high doses of beta carotene supplements in an attempt to prevent lung cancer and other cancers, the supplements were found to increase the risk of lung cancer in cigarette smokers, and a third study found neither benefit nor harm from them.76, –78 Therefore, consuming vegetables and fruits that contain beta carotene may be helpful, but high-dose beta carotene supplements should be avoided.
What are bioengineered foods, and are they safe? Bioengineered foods are made by adding genes from other plants or organisms to increase a plant's resistance to insect pests, retard spoilage, or improve transportability, flavor, nutrient composition, or other desired qualities. In theory, these added genes might create substances that could cause adverse reactions among sensitized or allergic individuals. However, there is currently no evidence that the substances found in bioengineered foods now on the market are harmful or that they would either increase or decrease cancer risk because of the added genes.
Is calcium related to cancer? Several studies have suggested that foods high in calcium might help reduce the risk for colorectal cancer,163 and calcium supplementation modestly reduces the formation of colorectal adenomas.126,127 There is also evidence, however, that a high calcium intake, primarily through supplements, is associated with increased risk for prostate cancer, especially for prostate cancers that are more aggressive.131 In light of this, both men and women should strive to consume recommended levels of calcium, primarily through food sources. Recommended intake levels of calcium are 1,000 mg/day for people aged 19 to 50 and 1,200 mg/day for people older than 50 years.164 Dairy products are excellent sources of calcium, as are some leafy vegetables and greens. People who obtain much of their calcium from dairy products should select low-fat or nonfat choices to reduce intake of saturated fat.
Does cholesterol in the diet increase cancer risk? Cholesterol in the diet comes only from foods derived from animal sources—meat, dairy products, eggs, and animal fats such as butter or lard. Although some of these foods (eg, processed and red meats) are associated with higher risk of certain types of cancer, at present, there is little evidence that this increased risk is specifically related to cholesterol. Lowering blood cholesterol lowers cardiovascular disease risk, but there is no evidence that lowering blood cholesterol has an effect on cancer risk.
Does drinking coffee cause cancer? No. Caffeine may heighten symptoms of fibrocystic breast lumps (a type of benign breast disease) in some women, but there is no evidence that it increases the risk of breast cancer or other types of cancer. The association between coffee and pancreatic cancer, widely publicized in the past, has not been confirmed by recent studies; there does not appear to be any connection between coffee drinking and cancer risk.165
Will eating less fat lower cancer risk? There is little evidence that the total amount of fat consumed increases cancer risk. However, diets high in fat tend to be high in calories and may contribute to obesity, which in turn is associated with increased risk of cancers at several sites. There is evidence that certain types of fat, such as saturated fats, may have an effect on increasing cancer risk.97 There is little evidence that other types of fat (omega-3 fatty acids, found primarily in fish), monounsaturated fatty acids (found in olive and canola oils), or other polyunsaturated fats reduce cancer risk.
What is dietary fiber, and can it prevent cancer? Dietary fiber includes a wide variety of plant carbohydrates that are not digestible by humans. Specific categories of fiber are “soluble” (like oat bran) or “insoluble” (like wheat bran and cellulose). Soluble fiber helps to reduce blood cholesterol and, therefore, helps lower the risk of coronary heart disease. Good sources of fiber are beans, vegetables, whole grains, and fruits. Associations between fiber and cancer risk are weak, but consumption of these foods is still recommended because they contain other nutrients that may help reduce cancer risk and because of their other health benefits.15
Does eating fish protect against cancer? Fish is a rich source of omega-3 fatty acids. Studies in animals have found that these fatty acids suppress cancer formation or hinder cancer progression, but there is limited suggestive evidence of a possible benefit in humans.166 While consuming fish rich in omega-3 fatty acids is associated with reduced risk of cardiovascular disease, some types of fish may contain high levels of mercury, polychlorinated biphenyls (PCBs), dioxins, and other environmental pollutants. Levels of these substances are generally highest in older, larger, predatory fish such as swordfish, tilefish, shark, and king mackerel. (In addition, some studies have shown that farm-raised fish may carry more of these toxins than fish caught in the wild.) Women who are pregnant, planning to become pregnant, or who are nursing, and young children should not eat these fish.167 Consumers should be advised to vary the types of fish consumed to reduce the likelihood of exposure to excessive levels of toxins.
Research has not yet demonstrated whether the possible benefits of fish consumption may be reproducible by taking omega-3 or fish oil supplements.
Do fluorides cause cancer? No. Extensive research has examined the effects of fluorides given as dental treatments, or added to toothpaste, public water supplies, or foods on cancer risk. Fluorides have not been found to increase cancer risk.168
What is folate, and can it prevent cancer? Folate is a B vitamin found in many vegetables, beans, fruits, whole grains, and fortified breakfast cereals. Since 1998, all grain products have been fortified with folate. Folate deficiency may increase the risk of cancers of the colorectum and breast, especially in people who consume alcoholic beverages.106, –108,169 Current evidence suggests that to reduce cancer risk, folate is best obtained through consumption of vegetables, fruits, and enriched grain products.
Do food additives cause cancer? Many substances are added to foods to preserve them and to enhance color, flavor, and texture. New additives must be cleared by the Federal Drug Administration before being incorporated into the food supply, and rigorous testing in animal models to determine any effects on cancer is undertaken as part of this process.170 Additives are usually present in very small quantities in food, and no convincing evidence exists that any additive consumed at these levels causes human cancers.
Can garlic prevent cancer? The health benefits of the Allium compounds contained in garlic and other vegetables in the onion family have been publicized widely. Garlic is currently under study for its ability to reduce cancer risk. Insufficient evidence exists at this point to support a specific role for this vegetable in cancer prevention.171,172
If our genes determine cancer risk, how can diet help prevent cancer? Damage to the genes that control cell growth and maturation can either be inherited or acquired during one's lifetime. Certain types of mutations or genetic damage can increase the risk of cancer. Nutrients in the diet can protect DNA from being damaged. Physical activity, weight control, and diet might delay or prevent the development of cancer in people with an increased genetic risk for cancer. The many interactions between diet and genetic factors are an important and complex topic of widespread current research interest.
Do irradiated foods cause cancer? No. Radiation is increasingly used to kill harmful organisms on foods to extend their “shelf life.” Radiation does not remain in the foods after treatment, however, and at the present time, there is no evidence that consuming irradiated foods increases cancer risk.173,174
Will lycopene reduce cancer risk? Lycopene is the red-orange carotene pigment found primarily in tomatoes and tomato-based foods, and to a lesser extent, in pink grapefruit and watermelon. Several studies have reported that consumption of tomato products reduces the risk of some cancers.149,175 It is uncertain, however, whether lycopene is the micronutrient responsible for this association. It is important to note that even if lycopene in foods is associated with lower risk for cancer, the conclusion cannot be made that high doses taken as supplements would be either more effective or safe.
Meat: Cooking and Preserving
Should I avoid processed meats? Some epidemiologic studies have linked high consumption of processed meats with increased risk of colorectal and stomach cancers.93, –95,154 This association may or may not be due to nitrites, which are added to many luncheon meats, hams, and hot dogs to maintain color and to prevent contamination with bacteria. Consumption of processed meats and meats preserved by methods involving smoke or salt increases exposure to potentially carcinogenic chemicals, and so should be minimized.
How does cooking meat affect cancer risk? Adequate cooking is necessary to kill harmful microorganisms within meat. However, some research suggests that frying, broiling, or grilling meats at very high temperatures creates chemicals that might increase cancer risk. Although studies show that these chemicals can damage DNA and cause cancer in animals, it is not clear how much they, rather than other components of meat, contribute to the increase in colorectal cancer risk associated with heavier meat consumption in epidemiologic studies. Techniques such as braising, steaming, poaching, stewing, and microwaving meats minimize the production of these chemicals.
Does being overweight increase cancer risk? Yes. Overweight and obesity are associated with increased risk for cancers of the breast among postmenopausal women, colon, endometrium, gallbladder, adenocarcinoma of the esophagus, pancreas, renal cell (kidney) carcinoma, and possibly other sites as well.3,27, , –30,33,176 Although there is limited research on whether losing weight reduces cancer risk, some research suggests that weight loss does reduce the risk of breast cancer.36,38 Because of other proven health benefits to losing weight, people who are overweight are encouraged to stop gaining weight, then to lose weight and prevent regaining it. The avoidance of excessive weight gain during adulthood is important not only to reduce cancer risk, but the risk of other chronic diseases as well.13,14
Does olive oil affect cancer risk? Consumption of olive oil is associated with a reduced risk of cardiovascular disease, but it is not associated with any increased risk of cancer and is most likely neutral with respect to cancer risk. Although olive oil is a healthy alternative to butter and margarine, it is a significant source of calories and should be used in moderation.
Are foods labeled organic more effective in lowering cancer risk? The term organic is popularly used to designate plant foods grown without pesticides and genetic modifications. At present, no research exists to demonstrate whether such foods are more effective in reducing cancer risk than are similar foods produced by other farming methods.
Pesticides and Herbicides
Do pesticides in foods cause cancer? Pesticides and herbicides can be toxic when used improperly in industrial, agricultural, or other occupational settings. Although vegetables and fruits sometimes contain low levels of these chemicals, overwhelming scientific evidence supports the overall health benefits and cancer-protective effects of eating vegetables and fruits.11 At present, there is no evidence that residues of pesticides and herbicides at the low doses found in foods increase the risk of cancer. However, produce should be thoroughly washed before consumption.
Will increasing physical activity lower cancer risk? Yes. People who engage in moderate to vigorous levels of physical activity are at lower risk of developing colon and breast cancer than those who do not.3,53,122 For some cancers, this risk reduction is independent of the impact of activity on weight. Data for a direct effect on the risk of developing other cancers are more limited. Nonetheless, overweight and obesity have been associated with many types of cancer,3 and physical activity is a key component of maintaining or achieving a healthy body weight. In addition, physical activity has a beneficial impact on cardiovascular disease and diabetes.15
What are phytochemicals, and do they reduce cancer risk? The term phytochemicals refers to a wide variety of compounds produced by plants. Some of these compounds protect plants against insects or have other biologically important functions. Some have either antioxidant or hormone-like actions both in plants and in people who eat them.177 Because consumption of vegetables and fruits reduces cancer risk, researchers are searching for specific components that might account for the beneficial effects. There is no evidence that phytochemicals taken as supplements are as beneficial as the vegetables, fruits, beans, and grains from which they are extracted.
Does saccharin cause cancer? No. High doses of the artificial sweetener saccharin cause the formation of bladder stones that can lead to bladder cancer in rats. Saccharin consumption does not cause the formation of bladder stones in humans, though. Saccharin has been removed from the list of established human carcinogens by the US National Toxicology Program.178
Do high levels of salt in the diet increase cancer risk? Studies in other countries link diets containing large amounts of foods preserved by salting (ie, salt-curing) and pickling with an increased risk of stomach, nasopharyngeal, and throat cancer. No evidence suggests that moderate levels of salt used in cooking or in flavoring foodsaffect cancer risk.
What is selenium, and can it reduce cancer risk? Selenium is a mineral that contributes to the antioxidant defense mechanisms. Animal studies suggest that selenium protects against cancer, and one experimental trial has shown selenium supplements might reduce the risk of cancers of the lung, colon, and prostate.179 However, repeated and well-controlled studies are needed to confirm whether selenium is helpful in preventing these cancers. High-dose selenium supplements are not recommended, as there is only a narrow margin between safe and toxic dosages. The maximum dose in a supplement should not exceed 200 micrograms per day.
Can soy-based foods reduce cancer risk? Soy-derived foods are an excellent source of protein and a good alternative to meat. Soy contains several phytochemicals, some of which have weak estrogenic activity and appear to protect against hormone-dependent cancers in animal studies. Presently, there are limited data to support a potential beneficial effect of soy supplements on reducing cancer risk.180 Furthermore, adverse effects of high doses of soy supplements on the risk of estrogen-responsive cancers, such as breast or endometrial cancer, are possible.181 Breast cancer survivors should consume only moderate amounts of soy foods as part of a healthy plant-based diet, and they should not intentionally ingest very high levels of soy products in their diet or more concentrated sources of soy, such as soy-containing pills, powders, or supplements containing isolated or concentrated isoflavones.
Does sugar increase cancer risk? Sugar increases caloric intake without providing any of the nutrients that reduce cancer risk. By promoting obesity and elevating insulin levels, high sugar intake may indirectly increase cancer risk. White (refined) sugar is no different from brown (unrefined) sugar or honey with regard to these effects on body weight or insulin. Limiting foods such as cakes, candy, cookies, and sweetened cereals, as well as high-sugar beverages such as soda, can help reduce sugar intake.
Can nutritional supplements lower cancer risk? There is strong evidence that a diet rich in vegetables, fruits, and other plant-based foods may reduce the risk of cancer, but there is no evidence at this time that supplements can reduce cancer risk, and some evidence exists that indicates that high-dose supplements can increase cancer risk.182,183
Can I get the nutritional equivalent of vegetables and fruits in a pill? No. Many healthful compounds are found in vegetables and fruits, and it is likely that these compounds work synergistically to exert their beneficial effect. There are likely to be important, but as yet unidentified, components of whole food that are not included in supplements. The small amount of dried powder in the pills that are represented as being equivalent to vegetables and fruits frequently contains only a small fraction of the levels contained in the whole foods. Food is the best source of vitamins and minerals. Supplements, however, may be beneficial for some people, such as pregnant women, women of childbearing age, and people with restricted dietary intakes. If a supplement is taken, the best choice is a balanced multivitamin/mineral supplement containing no more than 100% of the “Daily Value” of most nutrients.
Can drinking tea reduce cancer risk? Some researchers have proposed that tea might protect against cancer because of its antioxidant content. In animal studies, some teas (including green tea) have been shown to reduce cancer risk,184,185 but epidemiologic studies have had mixed findings.186,187 Presently, tea has not been proven to reduce cancer risk in humans.
Do trans-saturated fats increase cancer risk? Trans-saturated fats are produced during the manufacture of hydrogenated oils such as margarine or shortening to make them solid at room temperature. Recent evidence demonstrates that trans-fats have adverse cardiovascular effects, such as raising blood cholesterol levels.13,188 Their relationship to cancer risk, however, has not been determined. Regardless, it is recommended to consume as few trans-fats as possible.
Vegetables and Fruits
Will eating vegetables and fruits lower cancer risk? Yes. Greater consumption of vegetables and fruits has been associated in the majority of epidemiologic studies with a lower risk of lung, oral, esophageal, stomach, and colon cancer.11 Because it is not known which of the many compounds in vegetables and fruits are most protective, the best advice is to consume five or more servings of a variety of colorful vegetables and fruits each day.
What are cruciferous vegetables, and are theyimportant in cancer prevention? Cruciferous vegetables belong to the cabbage family, and include broccoli, cauliflower, Brussels sprouts, and kale. These vegetables contain certain chemicals thought to reduce the risk for colorectal cancer. The best evidence suggests that consumption of a wide variety of vegetables, including cruciferous and other vegetables, reduces cancer risk.11,12
Is there a difference in the nutritional value of fresh, frozen, and canned vegetables and fruits? Yes, but they can all be good choices. Fresh foods are usually considered to have the most nutritional value. Often, however, frozen foods can be more nutritious than fresh foods because they are often picked ripe and quickly frozen; nutrients can be lost in the time between harvest and consumption for fresh foods. Canning is more likely to reduce the heat-sensitive and water-soluble nutrients because of the high heat temperatures necessary in the canning process. Be aware that some fruits are packed in heavy syrup, and some canned vegetables are high in sodium. Choose vegetables and fruits in a variety of forms.
Does cooking affect the nutritional value of vegetables? Boiling vegetables, especially for long periods, can leach their content of water-soluble vitamins. Microwaving and steaming are the best ways to preserve the nutritional content in vegetables.
Should I be juicing my vegetables and fruits? Juicing can add variety to the diet, and it can be a good way to consume vegetables and fruits, especially for those who have difficulty chewing or swallowing. Juicing also improves the body's absorption of some of the nutrients in vegetables and fruits. However, juices may be less filling than whole vegetables and fruits and contain less fiber. Fruit juice, in particular, can contribute quite a few calories to one's diet if large amounts are consumed. Commercially juiced products should be 100% vegetable or fruit juices and should be pasteurized to eliminate harmful microorganisms.
Do vegetarian diets reduce cancer risk? Vegetarian diets include many health-promoting features; they tend to be low in saturated fat and high in fiber, vitamins, and phytochemicals.189 It is not possible to conclude at this time, however, that a vegetarian diet has any special benefits for the prevention of cancer. Diets including lean meats in small to moderate amounts can also be healthful. Strict vegetarian diets that avoid all animal products, including milk and eggs, should be supplemented with vitamin B12, zinc, and iron (especially for children and premenopausal women).189
Does vitamin A lower cancer risk? Vitamin A (retinol) is obtained from foods in two ways: preformed from animal food sources, and derived from beta carotene in plant-based foods. Vitamin A is needed to maintain healthy tissues. Vitamin A supplements, whether in the form of beta carotene or retinol, have not been shown to lower cancer risk, and high-dose supplements may, in fact, increase the risk for lung cancer in current and former smokers.76,77
Does vitamin C lower cancer risk? Vitamin C is found in many vegetables and fruits, particularly oranges, grapefruit, and peppers. Many studies have linked consumption of vitamin C–rich foods with a reduced risk for cancer.11 The few studies in which vitamin C has been given as a supplement, however, have not shown a reduced risk for cancer.
Does vitamin D lower cancer risk? There is a growing body of evidence from epidemiologic studies (not yet tested in RCTs) that vitamin D may have beneficial effects on some types of cancer, including cancers of the colon, prostate, and breast.190 Vitamin D is obtained through skin exposure to ultraviolet (UV) radiation, and through diet, particularly products fortified with vitamin D such as milk and cereals, and supplements. Many Americans, however, do not consume sufficient amounts of vitamin D.191 The current national recommended levels of intake of vitamin D of 200 to 600 IU164 may be inadequate to meet needs, especially among those with little sun exposure, the elderly, individuals with dark skin, and exclusively breast-fed babies. More research is needed to define optimal blood and intake levels for cancer risk reduction, but recommended intake is likely to fall between 200 and 2000 IU, depending on age and other factors that modify vitamin D status. To minimize the health risks associated with UVB radiation exposure while maximizing the potential benefits of optimum vitamin D levels, a balanced diet, supplementation, and limiting sun exposure to small amounts are the preferred methods of obtaining vitamin D.
Does vitamin E lower cancer risk? Alpha-tocopherol is recognized as the most active form of vitamin E in humans and is a powerful biological antioxidant. A reduction in prostate cancer incidence was observed among men randomly assigned to receive alpha-tocopherol in the Alpha-Tocopherol Beta Carotene (ATBC) trial, a study that included only male smokers.76 However, this association was not observed in the HOPE-TOO trial,192 in postintervention follow up of the ATBC trial,193 or in two large prospective observational studies,194,195 and may have been a result of chance. While ongoing randomized trials196,197 will eventually provide further information, the promise of alpha-tocopherol as a cancer prevention agent appears to be dimming.
Water and Other Fluids
How much water and other fluids should I drink? Consumption of water and other liquids may reduce the risk of bladder cancer, as water dilutes the concentration of carcinogens and shortens the time in which they are in contact with the bladder lining.111 Some studies suggest that adequate fluid consumption may also reduce the risk of colon cancer.198 Drinking at least 8 cups of liquid a day is usually recommended, and some studies indicate that even more may be beneficial.
ACS 2006 NUTRITION AND PHYSICAL ACTIVITY GUIDELINES ADVISORY COMMITTEE
Volunteer Members: Barbara Ainsworth, PhD, MPH; Professor, Exercise and Nutritional Science, Cancer Prevention and Control Program, San Diego State University; Rachel Ballard-Barbash, MD, MPH; Associate Director, Applied Research Program, Division of Cancer Prevention and Control, National Cancer Institute, Rockville, MD; Elisa V. Bandera, MD, PhD; Assistant Professor, The Cancer Institute of New Jersey, New Brunswick, NJ; Abby F. Bloch, PhD, RD, FADA; Nutrition Consultant, New York, NY; Tim Byers, MD, MPH; Professor, Department of Preventive Medicine and Biometrics; and Deputy Director, University of Colorado Cancer Center, Aurora, CO; June M. Chan, ScD; Assistant Professor and Program Director, Genitourinary Cancer Epidemiology and Population Science, University of California, San Francisco; Ralph J. Coates, PhD; Associate Director for Science, Division of Cancer Prevention and Control, Centers for Disease Control and Prevention (CDC), Atlanta, GA; Wendy Demark–Wahnefried, PhD, RD, LDN; Professor, Surgery and School of Nursing, Duke University Medical Center, Durham, NC; Jo Freudenheim, PhD; University of Buffalo Distinguished Professor and Chair, Department of Social and Preventive Medicine, School of Public Health and Health Professions, University at Buffalo, State University of New York; Peter Gann, MD, ScD; Professor and Director of Pathology Research, Department of Pathology, College of Medicine, University of Illinois at Chicago; Edward Giovannucci, MD, ScD; Professor of Nutrition and Epidemiology, Harvard School of Public Health, Boston, MA; Terry Hartman, PhD, MPH, RD; Associate Professor, Nutrition, The Pennsylvania State University, University Park, PA; Laurence Kolonel, MD, PhD; Deputy Director, Cancer Research Center, University of Hawaii, Honolulu, HI; Lawrence H. Kushi, PhD; Associate Director for Etiology and Prevention Research, Kaiser Permanente, Oakland, CA; Alice H. Lichtenstein, DSc; Gershoff Professor of Nutrition Science and Policy; and Director and Senior Scientist, Tufts University, Boston, MA; Maria Elena Martinez, PhD, RD; Associate Professor of Public Health, Arizona Cancer Center, Tucson, AZ; Anne McTiernan, MD, PhD; Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA; Marion Morra, MA, ScD; President, Morra Communications, Milford, CT; Arthur Schatzkin, MD, DrPH; Chief, Nutrition Epidemiology Branch, National Cancer Institute, Bethesda, MD; Marty Slattery, PhD, MPH; Professor, Family and Preventive Medicine, School of Medicine, University of Utah, Salt Lake City, UT; Stephanie Smith-Warner, PhD; Assistant Professor of Nutritional Epidemiology, Department of Nutrition, Harvard School of Public Health, Boston, MA; Judith Wylie-Rosett, EdD, RD; Professor of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY; Wei Zheng, MD, PhD; Professor, Vanderbilt-Ingram Cancer Center, Nashville, TN
American Cancer Society Staff Members: Terri Ades, RN, MS, AOCN; Director, Cancer Information; Kimberly S. Andrews, Research Associate, Cancer Control Science; Vilma Cokkinides, PhD; Program Director, Risk Factor Surveillance; Colleen Doyle, MS, RD; Director, Nutrition and Physical Activity; Ted Gansler, MD, MBA; Director of Medical Content; Marji McCullough, ScD, RD; Nutritional Epidemiologist; Alicia Samuels, MPH; Manager, Medical and Scientific Communication; David P. Ringer, PhD, MPH; Scientific Program Director, Research Department; Robert A. Smith, PhD; Director of Cancer Screening; Michael J. Thun, MD, MS; Vice President, Epidemiology and Surveillance Research