Obesity and the Digestive System
Diet and exercise in management of obesity and overweight
According to World Health Organization, in 2010 there were over 1 billion overweight adults worldwide with 400 million adults who were obese. Obesity is a major risk factor for diabetes, cardiovascular disease, musculoskeletal disorders, obstructive sleep apnea, and cancers (prostate, colorectal, endometrial, and breast). Obese people may present to the gastroenterologists with gastroesophageal reflux, non-alcoholic fatty liver, and gallstones. It is important, therefore, to recognize and treat obesity.
The main cause of obesity is an imbalance between calories consumed and calories expended, although in a small number of cases, genetics and diseases such as hypothyroidism, Cushing's disease, depression, and use of medications such as antidepressants and anticonvulsants are responsible for fat accumulation in the body.
The main treatment for obesity is dieting, augmented by physical exercise and supported by cognitive behavioral therapy. Calorie-restriction strategies are one of the most common dietary plans. Low-calorie diet refers to a diet with a total dietary calorie intake of 800–1500, while very low-calorie diet has less than 800 calories daily. These dietary regimes need to be balanced in macronutrients, vitamins, and minerals. Fifty-five percent of the dietary calories should come from carbohydrates, 10% from proteins, and 30% from fats, of which 10% of total fat consist of saturated fats. After reaching the desired body weight, the amount of dietary calories consumed can be increased gradually to maintain a balance between calories consumed and calories expended. Regular physical exercise enhances the efficiency of diet through increase in the satiating efficiency of a fixed meal, and is useful for maintaining diet-induced weight loss. A meta-analysis by Franz found that by calorie restriction and exercise, weight loss of 5–8.5 kg was observed 6 months after intervention. After 48 months, a mean of 3–6 kg was maintained.
In conclusion, there is evidence that obesity is preventable and treatable. Dieting and physical exercise can produce weight loss that can be maintained.
Since 1980, obesity has more than doubled globally and is now considered as a major health hazard and a global epidemic. This review aims to evaluate the current management of obesity and overweight employing a combination of dietary interventions, exercise, and behavioral modification. For some patients, pharmacological therapy or bariatric surgery is required.
Definition of obesity
Obesity can be defined as an excessive amount of fat that increases the risk of medical illness and premature death. A simple and convenient way of defining obesity and overweight led by the World Health Organization (WHO) and the National Institute of Health (NIH) is based on body mass index (BMI).
BMI is derived by dividing one's weight in kilograms by the square of one's height in meters. Classification of overweight and obesity is based on data gathered from population-based epidemiology studies that evaluated the relationship between obesity and rates of mortality and morbidity that are adiposity related. A BMI (kg/m2) between 25 and 29.9 is deemed to be overweight. Obesity is defined as BMI ≥ 30 and is further subdivided into Class I–III. There is some evidence to suggest that risks of adiposity-related complications occur at lower BMIs in Asians. Hence, China used a BMI of 28 for obesity and Japan used a BMI cut-off of 25 kg/m2 for cut-off. The WHO has recommended that BMI > 27.5 kg/m2 be used as a cutoff for Asians, taking into consideration the increased cardiovascular risk at the BMI.
Health consequences of obesity
On average, obesity reduces life expectancy by 6 to 7 years: a BMI of 30–35 reduces life expectancy by 2–4 years while severe obesity (BMI > 40) reduces life expectancy by 10 years.
Complications of obesity are either directly caused by obesity or indirectly related through mechanisms sharing a common cause such as a sedentary life style or poor diet. The strongest link is with type 2 diabetics. Obesity accounts for 64% of cases of diabetics in men and 79% of cases in women. Other diseases attributable to obesity are cardiovascular disease—hypertension, stroke, coronary artery disease, venous stasis deep vein thrombosis, osteoarthritis, gastrointestinal disease, gastroesophageal reflux disease, cholelithiasis, non-alcoholic fatty liver disease (NAFLD), endometrial breast cancer, and colorectal cancer. Obesity is the leading cause of cancer just behind smoking. Metabolic disorders include metabolic syndrome, prediabetic state, hyperlipidemia, and polycystic ovary syndrome. Most patients with obstructive sleep apnea (OSA) are obese, although in lean persons, other factors such as cephalometric defects contributed to risk of OSA. In addition to BMI and waist circumference, it is important to look out for comorbidities that are associated with obesity such as diabetes, NAFLD, polycystic ovary syndrome, OSA, and osteoarthritis.
Clinical evaluation of obesity in adults: waist circumference
Central or truncal obesity, as measured by waist circumference, is also associated with increased risk for heart disease, diabetes mellitus, hypertension, and hyperlipidemia.
The WHO STEPwise approach to surveillance protocol for measuring waist circumference requires waist circumference to be measured at the midpoint between the lower margin of the palpable rib and the top of the iliac crest. The NIH, which provided the protocol for use in the National Health and National Examination Survey, determines that waist circumference be measured at the top of the iliac crest. Ethnic differences exist, and in Asia, waist circumference > 80 cm for females and > 90 cm for men are considered outside the normal range.
Establishing the cause of overweight and obesity
Although excessive food energy intake and a sedentary lifestyle account for most cases of overweight and obesity, it is important to recognize that medical illness and drug treatment of medical illness can increase the risk of obesity and are amenable to treatment. The neuroendocrine causes of obesity include hypothyroidism, Cushing's syndrome, growth hormone deficiency, hypogonadism, and polycystic ovary syndrome. Eating disorders, notably binge eating disorders and night eating syndrome, also give rise to obesity.
Obesity is not regarded as a psychiatric disorder, but the risk of obesity is increased in patients with psychiatric disorders such as depression. Medications that can cause weight gain include antidepressants, antidiabetic drugs, anticonvulsants, antipsychotic medication, beta-blockers, and steroid hormones. Cessation of smoking is associated with weight gain. It is important to note comorbidities associated with obesity: diabetes mellitus, hyperlipidemia, hypertension, and cardiovascular disease.
Medical treatment of overweight and obesity
The management of overweight and obesity is lifestyle intervention, consisting of dietary intervention, exercise, and behavioral treatment.
Setting a goal for weight loss
Setting a goal for weight loss is the first step in planning a weight loss program. The patient needs to accept that the goal is reasonable, realistic, and attainable. An initial weight loss of 5–7% of bodyweight within 6 months is achievable. The Diabetes Prevention Program is an example of a successful lifestyle intervention program that set the weight loss target of 7% of bodyweight.
Dietary intervention is the cornerstone of weight loss therapy. Most of the dietary regimens proposed for weight loss focus on energy content and macronutrient composition. It is the energy content that determines the efficiency of the dietary regimens. Obesity treatment guidelines issued by the NIH recommend that persons who are overweight or who have class I obesity and who have two or more risk factors should reduce their energy intake by 500 kcal/day. Persons with class II and class III obesity should strive for 500–1000 kcal/day reduction. With a reduction of 500 kcal/day energy intake, a weight reduction of 0.5 kg/week can be achieved.
To provide a diet that results in the desired energy deficit, it is necessary to determine the patient's daily energy requirement, which can be estimated by using the Harris–Benedict equation or the WHO equation or American Gastroenterological Association dietary guidelines.
Type of diets
In general, there are four types of dietary regimens used in the treatment of the overweight or obese persons: (Table 1)
- Low-calorie diet (LCD)
- Low-fat diet
- Low-carbohydrate diet
- Very low-calorie diet (VLCD)
Table 1. Comparison of different weight-loss diets[13-19]
|Low calorie|| |
55–60% carbohydrate (high fiber, low GI)
< 30% fat
|∼ 10% in 3–12 months||Reduction in blood glucose, TG, LDL, BP||Compliance difficult in long term|
|Low fat|| |
|∼ 5% in 2–12 months||Reduction in blood glucose, LDL, BP|| |
Less palatable, feel hungry easily
|Low carbohydrate|| |
60–150 g of carbohydrate
< 60 g (very low carbohydrate)
|∼ 5% in 2–12 months|| |
Faster initial weight loss than low-fat diets
Reduced blood glucose, TG, LDL, BP
|Ketosis when carbohydrate intake < 50 g/day|
|Very low-calorie diet|| |
55–60% carbohydrate (high fiber, low GI)
< 30% fat
|> 10% in 2–8 weeks||Rapid weight loss|| |
Electrolyte imbalance, hypotension, gallstones
Needs medical supervision
The first three diets are 800–1500 kcal/day while VLCD is < 800 kcal/day.
LCDs are high in carbohydrate (55–60%), low in fat (less than 30% of energy intake), and high in fiber and have a low-glycemic index. Alcohol and energy-dense snacks should be avoided. LCD has been shown in 34 randomized trials to reduce body weight by 8% during 3–12-month period. Overweight or obese patients tend to underestimate their energy intake. To help them overcome this, portion-controlled or prepackaged meals that make up the required energy intake are available. Replacement meals are available as drinks, nutrition bars, or prepackaged meals. A 4-year study demonstrated weight loss improvement in blood sugar and blood pressure for persons taking meal replacement diets.
These diets reduce the daily intake of fat to 20–25% of total energy intake. For a person on a 1500-calorie diet, this translates to 30–37 g of fat, which can be counted using food label from packages. Alternatively, a dietician can provide the person with a specific menu plan that has reduced fat.
According to a meta-analysis of 16 trials, low-fat diet used over 2–12 months resulted in mean weight loss of 3.2 kg and improved cardiovascular risk factors (Table 1).
The carbohydrate content of the diet is an important determinant of short-term (less than 2 weeks) weight loss. Low-carbohydrate (60–150 g of carbohydrate/day) and very low-carbohydrate diet (0 to < 60 g) have been popular for many years. Glycogen utilization occurs when carbohydrate intake is restricted. When the carbohydrate intake is less than 50 g/day, ketosis will develop from glycogenolysis, resulting in fluid loss. Many of the current low-carbohydrate diets (e.g. Atkins diet) limit carbohydrate intake to 20 g/day but allow unrestricted amounts of fat and protein. A meta-analysis of five trials found that weight loss at 6 months favoring low-carbohydrate over low-fat diet is not sustained at 12 months. Triglycerides and high-density lipoprotein (HDL) cholesterol changed more favorably in people assigned to low-fat diet. There are data from the National Health Study and Health Professional, Follow Up study that low-carbohydrate diet with the highest decile for animal protein and fat were associated with higher all-cause and cardiovascular mortality.
VLCDs are diets with energy content of 200–800 kcal/day. Diets below 200 kcal/day are starvation diets. VLCDs are not recommended for general use, as there are significant adverse events such as electrolyte unbalance, low blood pressure, and increased risk of gallstones. Its use needs to be supervised by trained medical personnel.
Each of the four types of diet for weight loss has its proponents. In a meta-analysis of 80 weight loss studies, mean weight loss of 5 to 8.5 kg (5–9%) was observed during the first 6 months from interventions involving a reduced-energy diet and/or weight loss medications with weight plateaus at approximately 6 months, with maintenance of 3 to 6 kg (3–6%) of weight loss at 48 months. A randomized controlled trial comparing four weight loss diets with different compositions of fat, carbohydrate and protein found no difference in outcomes, with a 2- to 4-kg weight loss with all diets after a year. After 2 years, all calorie-restricted diets result in equal weight loss irrespective of the macronutrient composition. In contrast, all studies found that dietary adherence is an important determinant of weight loss.[13-19] Thus, choosing a diet with a macronutrient composition based on a subject's taste preference can achieve better compliance.
Exercise and obesity
Physical activity alone is not an effective method for achieving initial weight loss, although most overweight or obese people tend to choose exercise as the first interventional option. Without calorie restriction, weight loss through exercise alone is quite small, about 0.1 kg/week. A meta-analysis showed that exercise alone did not result in significant weight loss attempts, although no further weight gain was observed after 12 months. Although exercise is not effective for initial weight loss, physical activity is important for maintaining weight loss achieved through dietary intervention. Meta-analyses of 493 studies have shown that people who diet and exercise maintained their weight loss better than those who relied on diet alone. Before starting an exercise program, patients should be advised of joint and musculoskeletal injuries as well as cardiovascular risks. The risk of exercise stress testing before an exercise program is controversial. The American College of Cardiology and American Heart Association recommend treadmill for asymptomatic subjects with diabetes mellitus, men older than 45 years of age, and women older than 55 years of age before embarking on an exercise program. Other organizations recommend no stress testing for symptomatic subjects undergoing moderate-intensity exercise with guidance in exercise intensity. In our hospital, we use a physical exercise readiness questionnaire for screening purposes.
The American College of Sports Medicine recommended in 2009 that moderate-intensity exercising between 150 and 250 min weekly is effective in preventing weight gain. To provide and maintain a clinically significant weight loss, at least 200–300 min/week of moderate-intensity aerobic exercise is required. Resistance training does not enhance weight loss but may increase fat-free mass. Even in the absence of significant weight loss, regular aerobic and resistance exercise improves cardiovascular fitness and obesity-related comorbidities such as NAFLD. A supervised exercise program involving personal trainers induces and maintains weight loss more effectively than unsupervised physical activity. Exercise reduces food intake by increasing the satiating efficiency of a fixed meal.
NAFLD patients are usually overweight or obese and have underlying insulin and or leptin resistance leading to dysfunctional energy metabolism. Weight loss of 10% in overweight NAFLD patients improves liver biochemistry as well as hepatic steatosis and necroinflammation. Lifestyle modification consisting of exercise and diet can help the patients to achieve these goals. A 4–4.5% weight loss can result in 50% reduction in serum alanine aminotransferase, while with exercise alone and no weight loss, significant improvement in aminotransferase levels can occur, but its effect on liver histology is unknown. The American Association for the Study of Liver Diseases, the American College of Gastroenterology, and the American Gastroenterology Association recommend weight loss as the preferred method in management of NAFLD.
Bariatric surgery is defined as gastrointestinal surgery to help severely obese patients lose weight. The US National Institutes of Health's 2013 guidelines recommended surgery for adults with BMI ≥ 40 kg/m2 without comorbidities or 35 kg/m2 with comorbidities who fail to lose weight by nonsurgical methods, and suggested that patients with BMI of 30–34.9 kg/m2 with diabetes or metabolic syndrome may also be offered a bariatric procedure, although current evidence is limited by the lack of long-term data demonstrating net benefit. A recent Asian Consensus Meeting on Metabolic Surgery also recommended that the BMI cutoffs be lowered to 35 and 32.5, respectively, and that surgery be considered for Asian adults with BMI ≥ 30 kg/m2 and central obesity (WC > 80 cm in females or > 90 cm in males) and at least two features of metabolic syndrome (raised triglycerides, low HDL cholesterol, hypertension, high-fasting plasma glucose). Gastric banding is a reversible restrictive procedure, while laparoscopic sleeve gastrectomy, Roux-en-Y gastric bypass, and bilio-pancreatic diversion combine restrictive and malabsorptive effects that produce 15–35% loss of baseline weight and improve other comorbidities.
Overweight and obesity are increasing at an alarming rate globally and has reached epidemic proportions in almost every country. Obesity has a significant contribution toward cardiovascular diseases, metabolic disorders, gastrointestinal disorders, and cancers. Yet in early stages of weight gain, when a person is overweight, its progression to morbid obesity can be arrested through diet and exercise, without the need for medication, endoscopic, or surgical procedures. We have attempted to put further evidence in support of current best practices in dietary management and exercise.
Finally, we conclude with two mnemonics that some of our team members found useful in clinical practice. Factors that contribute to obesogenic state are
- Diseases—hypothyroidism, Cushing's disease
- Drugs—corticosteroids, antidepressants, antipsychotics
- Diet—intake > activity
- Drink—beer, wine, sugar drinks
- Decreased—physical activity
- Depression and psychosocial
An ABCDE approach to obesity:
- For measurement of cardiovascular risk and comorbidity
- For blood pressure control
- For cholesterol management
- For diet control and text for diabetes
- For exercise therapy