VITAMIN D DEFICIENCY AND RISK FOR CESAREAN SECTION
Merewood A, Mehta SD, Chen TC, Bauchner H, and Holick MF. Association between vitamin D deficiency and primary cesarean section. J Clin Endocrinol Metab. 2009;94:940–945.
At the beginning of the 20th century, increased industrialization was associated with high levels of rickets. During this time, a common cause of death for women in childbirth was related to complications due to rachitic pelvis. Advances in cesarean section technique increased survival rates in these women. With the discovery of vitamin D and the subsequent fortification of milk with it, the incidence of rickets declined and rachitic malformations of the pelvis became less common. In recent years, vitamin D deficiency has again risen in prominence, and associated symptoms of vitamin D deficiency may have had an impact on the recent surge in cesarean deliveries. To examine this hypothesis, Merewood et al. measured maternal and infancy serum 25-hydroxyvitamin D [25(OH) D] levels and compared these values with type of delivery (cesarean or other).
Vitamin D deficiency was defined as serum levels of 25(OH) D < 37.5 nmol/L. Data from 253 women were included in the analysis. Of the total pool, 210 had vaginal deliveries and 67 had cesarean sections; 43 of the cesarean deliveries were via primary cesarean. When categorized as vitamin D-deficient or -non-deficient, 28% of the women with vitamin D deficiency had cesarean deliveries in comparison with only 14% of those with adequate vitamin D status. Regression analysis indicated that women with vitamin D deficiency were nearly four times as likely to have a primary cesarean delivery as those who had adequate vitamin D levels. There was a clear inverse relationship between vitamin D levels and cesarean delivery such that the women with the highest serum levels of 25(OH) D had the lowest probability of having a cesarean delivery. The authors indicate that widespread vitamin D deficiency is an ongoing and growing public health concern. Increasing vitamin D intake to raise blood levels of 25(OH) D above 37.5 nmol/L may help reduce the risk for a cesarean delivery.
WEIGHT MAINTENANCE DIETS AND CORONARY HEART DISEASE RISK FACTORS
Miller M, Beach V, Sorkin JD, Mangano C, Dobmeier C, Novacic D, Rhyne J, and Vogel RA. Comparative effects of three popular diets on lipids, endothelial function, and C-reactive protein during weight maintenance. J Am Diet Assoc. 2009;109:713–717.
Many popular weight-loss diets, including the Atkins diet and the Ornish plan, have been examined in recent years for their effects not only on weight loss itself, but also for effects on markers for heart disease and cardiovascular disease. The majority of this research focused upon weight-loss phases and little attention was given to the effects of these diets during the maintenance phase. Some research shows that over a year's time, weight loss resulting from low-carbohydrate, high-carbohydrate, and balanced diets tends to be the same across diets, but that some diets impact blood lipids and insulin levels differently. The present study described by Miller et al. examined changes in blood lipids and endothelial function in individuals following the maintenance portion of three popular diets: Atkins, South Beach, and Ornish.
All participants (N = 18; 50% women) completed 4 weeks of each diet with a 4-week washout period in between. As this study was measuring maintenance and not the effects of weight loss, all participants had a BMI of <30 when starting the dietary intervention phase; caloric intakes were adjusted if a participant had a change in body weight that exceeded 1.0 kg. Maintenance diets consisted of the Mediterranean-style maintenance phase of the South Beach diet, which emphasizes whole grains, complex carbohydrates, lean meats, nuts, fruits, and vegetables, the Atkins high-protein, high-fat, low-carbohydrate plan, which emphasizes meats, cheese, and some vegetables with limited carbohydrate intake, and the Ornish plan, which is a very-low-fat, high-carbohydrate plan. Fasting blood and brachial artery reactivity measurements were taken at baseline, and at the end of each 4-week interval (diet and washout). Primary outcome measures included total cholesterol, triglycerides, LDL and HDL cholesterol, C-reactive protein, and brachial artery flow-mediated vasodilation. Intake of cholesterol, total fat, and saturated fat was higher in the Atkins phase relative to the Ornish and South Beach phases of the study. The Atkins diet was associated with higher total cholesterol and LDL cholesterol relative to the other two plans, and reduced endothelial vasoreactivity relative to the Ornish plan. The authors conclude that high saturated fat intake, as typically seen with the Atkins plan, negatively impacts blood lipids and endothelial function during weight maintenance in healthy individuals. Blood lipids and endothelial function in these individuals were normal prior to dietary interventions, and were varied after the different dietary interventions. These findings are important in that they suggest any benefits in blood lipid profiles seen during active weight loss may not carry through to the maintenance phase of weight loss. The authors indicate that further research using these maintenance diets in individuals with visceral obesity, who may be at elevated risk for coronary heart disease, is warranted.
LINKS BETWEEN DIETARY FACTORS AND CORONARY HEART DISEASE
Mente A, de Koning L, Shannon HS, and Anand SS. A systematic review of the evidence supporting a causal link between dietary factors and coronary heart disease. Arch Intern Med. 2009;169:659–669.
The relationships between dietary factors and nutritional status and coronary heart disease have been researched extensively over the past 50 years. Data supporting links between diet and heart disease range from observational and epidemiological studies to cohort studies and randomized controlled trials. However, results from different trials can be contradictory, and randomized controlled trials have found some isolated nutrients to be harmful rather than protective, findings that are inconsistent with data from observational reports. Public health guidelines for diet and heart heath, which are informed by the best available evidence, are therefore complicated by a lack of consensus within the literature. The goal of the analysis conducted by Mente et al. was to provide a systematic review of the available literature examining the relationships between nutrient intake, dietary patterns, and dietary components (dietary exposures) and coronary heart disease.
The researchers conducted a Medline search for prospective cohort studies (n = 146) and randomized controlled trials (n = 43) investigating dietary exposures and coronary heart disease between 1950 and June 2007. The Bradford Hill guidelines were applied to each dietary exposure in cohort studies to derive a causation score for each dietary exposure, and were compared with randomized trials for consistency of effect. The Bradford Hill guidelines provide four criteria for evaluating cohort studies: strength, consistency, temporality, and coherence. Causation scores were derived from the sum of the number of criteria that were met ranging from 0 to 4. A score of 4 was considered strong evidence of a causal relationship between the dietary exposure and disease, a score of 3 indicated moderate evidence of causation, and scores ≤2 were considered weak evidence. A final criterion, experiment, was used to determine whether the evidence from cohort studies was consistent with evidence from randomized controlled trials. The authors identified causal relationships for strong protective factors, which include intake of nuts, vegetables, monounsaturated fats, and following Mediterranean, prudent, or high-quality diet patterns. Harmful factors included intake of trans-fats, high-glycemic-index foods, and following a Western dietary pattern. There was modest evidence to support a causal protective role for intake of whole grains, fish and marine oils, folate, dietary vitamins C, E, and beta carotene, alcohol, fruits, and fiber. There was weak evidence of causation (protective or harmful) for vitamins C and E taken in supplement form, eggs, milk, saturated and polyunsaturated fats, and meat. This large, systematic review provides evidence supporting a link between several dietary factors and coronary heart disease.
DIETARY SEAWEED AND ESTROGEN METABOLISM
Teas J, Hurley TG, Hebert JR, Franke AA, Sepkovic DW, Kurzer MS. Dietary seaweed modifies estrogen and phytoestrogen metabolism in healthy postmenopausal women. J Nutr. 2009 doi: 10.3945/jn.108.100834
Breast cancer incidence is lower in Japanese women than in US women. Japanese women who migrate to the United States see a rise in breast cancer incidence after 10 years of living in the country, suggesting that environmental and lifestyle differences play an important role in the risk for breast cancer. Consumption of phytoestrogens from soy in Japanese women has long been hypothesized to be important in the reduction of risk for breast cancer, and Japanese women consuming a traditional diet have a higher rate of estradiol excretion. Seaweed and sea vegetables are other common components of Japanese diets that are consumed less frequently in the United States. It is proposed that compounds found within seaweeds, such as alginate, fucoxanthin, and polyphenol compounds may all have strong anticancer properties. Additionally, seaweeds have a higher binding affinity for estrogens, and seaweed supplementation lowers serum estradiol. The study conducted by Teas et al. addressed the antiestrogenic ability of brown seaweed, Alaria esculenta, to modulate serum estrogen hormone levels and urinary excretion of estrogen metabolites and phytoestrogens both alone and in the presence of daily soy intake.
Using a randomized crossover design, 15 postmenopausal women were given 5 g/d Alaria or placebo for 7 weeks. During the final week, participants were also given soy isolate containing 2 mg isolflavones/kg. After a 3-week washout period, participants were crossed over to the other supplement schedule. Blood and urine samples were collected throughout the study. Primary outcome variables included urinary 2-hydroxyestrogen and 16α-hydroxyesterone, urinary phytoestrogen, and serum estrone, estradiol, and sex hormone-binding globulin. Supplementation with Alaria was inversely correlated with serum estradiol levels. Soy supplementation increased urinary excretion of phytoestrogens consistent with increased intake of phytoestrogens, and these increases were not affected by Alaria intake. Alaria plus soy increased excretion of 2-hydroxyestrogen and the ratio of 2-hydroxyestrogen:16α-hydroxyesterone. In seaweed-naïve women, supplementation with 5 g/d Alaria lowered serum estrogen levels and increased estrogen metabolism. Seaweeds alone have been shown to have anticancer properties, and in the present study seaweed showed protective effects in phytoestrogen and estrogen metabolism. The authors suggest that seaweed has promise for the dietary prevention of breast cancer.
LOW-GLYCEMIC BREAKFASTS AND FAT OXIDATION DURING EXERCISE
Stevenson EJ, Astbury NM, Simpson EJ, Taylor MA, and Macdonald IA. Fat oxidation during exercise and satiety during recovery are increased following a low-glycemic index breakfast in sedentary women. J Nutr. 2009;139:890–897.
A combination of diet and exercise is lauded as a means of keeping bodyweight in check. A single session of exercise can increase fat oxidation both during and up to 36 hours after exercise. Increased fat oxidation during exercise is an important consideration for those exercising for health or for weight maintenance. Fat oxidization is maximal when exercising in a fasted state; however, this is not always practical for the general population, and meals are usually consumed within several hours of exercise. In well-trained individuals, consumption of low-glycemic-index carbohydrates (CHO) prior to endurance exercise produces increased fat oxidation. To date, however, little is known about similar effects in conditions of low-intensity exercise or in untrained individuals. In the present study, Stevenson et al. measured substrate oxidation during low-intensity exercise in sedentary women, and how substrate oxidation changed as a function of the type of breakfast consumed. Additionally, they measured metabolic responses to a subsequent meal following exercise.
Eight healthy sedentary women completed two trials in a randomized crossover design. Women were provided test breakfasts of either high-glycemic-index (HGI) or low-glycemic-index (LGI) foods. Each meal provided 1 g CHO/kg and meals were matched for protein, fat, and carbohydrate content but not for fiber content (HGI: 1.5 g fiber; LGI: 3.5 g fiber). The calculated glycemic index was 78 for the HGI meal and 44 for the LGI meal. Meals consisted of standard breakfast foods including milk, fruit, yogurt, cereal, and bread. Breakfasts were given 3 hours prior to exercising for 60 minutes on a treadmill at 50% VO2 peak. Participants were provided a standard lunch of pasta with tomato sauce and cheese exactly 15 minutes after exercise. Blood samples were collected throughout the experimental time. Blood glucose and plasma peptide YY, ghrelin, and glucagon-like peptide (GLP-1) levels were determined. Energy expenditure and substrate oxidation were measured using an open-circuit indirect calorimeter. Mood and appetite were subjectively determined using visual analogue scales. Blood glucose and insulin concentrations were higher in the HGI condition relative to the LGI condition. Fat oxidation was suppressed during the 3-hour interval between breakfast and exercise, but was higher in the LGI condition compared to the HGI condition. Fat oxidation was greater during exercise in the LGI condition relative to the HGI condition, and satiety following lunch was greater in the LGI condition. The authors indicate that the glycemic index of the overall diet can be an important consideration in substrate oxidation, storage, and weight management.