Dietary fiber and body weight

OBJECTIVE: This review provides an update of recent studies of dietary fiber and weight and includes a discussion of potential mechanisms of how dietary fiber can aid weight loss and weight maintenance. METHODS: Human studies published on dietary fiber and body weight were reviewed and summarized. Dietary fiber content of popular low-carbohydrate diets were calculated and are presented. RESULTS: Epidemiologic support that dietary fiber intake prevents obesity is strong. Fiber intake is inversely associated with body weight and body fat. In addition, fiber intake is inversely associated with body mass index at all levels of fat intake after adjusting for confounding factors. Results from intervention studies are more mixed, although the addition of dietary fiber generally decreases food intake and, hence, body weight. Many mechanisms have been suggested for how dietary fiber aids in weight management, including promoting satiation, decreasing absorption of macronutrients, and altering secretion of gut hormones. CONCLUSION: The average fiber intake of adults in the United States is less than half recommended levels and is lower still among those who follow currently popular low-carbohydrate diets, such as Atkins and South Beach. Increasing consumption of dietary fiber with fruits, vegetables, whole grains, and legumes across the life cycle is a critical step in stemming the epidemic of obesity found in developed countries. The addition of functional fiber to weight-loss diets should also be considered as a tool to improve success.     

Dietary change,energy balance and body weight regulation among migrating students

This study was conducted to examine how subjects modulate their food intake and energy balance when they migrate from a low energy density food intake pattern to one of high energy density. It was hypothesised that an increase in the energy density of food consumed would result in increased body weight of the migrating subjects unless food intake and energy balance could be modulated. Food selection, food intake, basal metabolic rate (BMR) and anthropometric measurements were made on 53 female and 56 male newly arrived overseas students. All subjects were from Malaysia, but the data was collected at Oxford Brookes University where the subjects were studying. Food intake using 3-day food diaries and food frequency questionnaires (FFQs), BMR and anthropometric measurements including body weight were measured on arrival in the UK and after 3 and 6 months' stay. Student's t -tests and analysis of variance (ANOVA) were used to compare the data. A significant difference (P < 0.05) was found between the energy density of the foods consumed in Malaysia and after 3 and 6 months in the UK. There was also a significant decrease (P < 0.05) in protein consumed. However, there were no differences in total energy intake. From results of the FFQs, differences were found in food selection due mainly to the lack of availability of certain foods in UK supermarkets. No significant differences were found in the BMR and anthropometric measurements made at the start of the study and later assessments. It appears that Malaysian students are able to remain in energy balance and are weight stable at least during the first 6 months of residence in the UK, despite the wider choice of energy dense food available. This suggests that at least in the short term, subjects are able to modulate their food intake in response to changes in the energy densities and free choice of food.     

Dietary change, energy balance and body weight regulation among migrating students

This study was conducted to examine how subjects modulate their food intake and energy balance when they migrate from a low energy density food intake pattern to one of high energy density. It was hypothesised that an increase in the energy density of food consumed would result in increased body weight of the migrating subjects unless food intake and energy balance could be modulated. Food selection, food intake, basal metabolic rate (BMR) and anthropometric measurements were made on 53 female and 56 male newly arrived overseas students. All subjects were from Malaysia, but the data was collected at Oxford Brookes University where the subjects were studying. Food intake using 3-day food diaries and food frequency questionnaires (FFQs). BMR and anthropometric measurements including body weight were measured on arrival in the UK and after 3 and 6 months' stay. Student's t-tests and analysis of variance (ANOVA) were used to compare the data. A significant difference (P < 0.05) was found between the energy density of the foods consumed in Malaysia and after 3 and 6 months in the UK. There was also a significant decrease (P < 0.05) in protein consumed. However, there were no differences in total energy intake. From results of the FFQs, differences were found in food selection due mainly to the lack of availability of certain foods in UK supermarkets. No significant differences were found in the BMR and anthropometric measurements made at the start of the study and later assessments. It appears that Malaysian students are able to remain in energy balance and are weight stable at least during the first 6 months of residence in the UK, despite the wider choice of energy dense food available. This suggests that at least in the short term, subjects are able to modulate their food intake in response to changes in the energy densities and free choice of food.     

Dietary fiber and cancer

There is currently a great interest in the protective potential of β‐carotene and other micronutrients against carcinogenesis. We investigated the role of β‐carotene in modifying 7,12‐dimethylbenz[a]anthracene (DMBA)‐initiated, 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA)‐promoted, two‐stage skin carcinogenesis. We were interested in comparing the protective effects of two types of dietary β‐carotene, a beadlet formulation and crystalline β‐carotene, in two strains of mice (Skh:HR‐1 and CR:ORL Sencar). Mice were maintained throughout the study on one of these 3% β‐carotene‐fortified diets or on control diets. In Week 11 after the start of the diets, the DMBA/TPA treatment regimen was begun. The resulting skin tumors were counted weekly. In addition, serum and skin levels were monitored for β‐carotene at the time of chemical initiation and at the termination of the study. A decrease in the number of cumulative tumors in the β‐carotene‐fed animals compared with the appropriate control groups was observed in both strains of mice. However, statistical evaluation of the data revealed that the decrease was significant only in Skh mice. This phenomenon might be explained by the inherent sensitivity of Sencar mice to the two‐stage carcinogenesis treatment regimen. The mechanism of the protective effect found in this study is still not clear. Recent data suggest that a vitamin A pathway is not probable but that a direct ¹O2 and/or radical‐quenching property of the parent β‐carotene molecule may be involved. This study also demonstrates that tvo‐stage‐induced skin tumorigenesis can be modified by both types of β‐carotene‐fortified diets.     

Dietary proteins in the regulation of food intake and body weight in humans

This review presents 4 lines of evidence supporting a role for proteins in the regulation of food intake and maintenance of healthy body weights. It is concluded that the protein content of food, and perhaps its source, is a strong determinant of short-term satiety and of how much food is eaten. Although the role of protein in the regulation of long-term food intake and body weight is less clear, the evidence reviewed suggests that further research to define its role is merited. Such research has the potential to lead to new functional foods, food formulations, and dietary recommendations for achieving healthy body weights.     

Dietary fiber and fat are associated with excess weight in young and middle-aged US adults

OBJECTIVE: To examine relative associations of dietary composition variables with body mass index (BMI; calculated as kg/m2) among young and middle-aged US adults. We hypothesized that in subjects with physiologically plausible reported energy intakes, fiber intake would be inversely associated with BMI, independent of other dietary composition and sociodemographic variables. SUBJECTS AND DESIGN: Data from adults age 20 to 59 years in the Continuing Survey of Food Intakes by Individuals (CSFII) 1994-1996 were used. Exclusions were pregnancy or lactation, food insecurity, missing weight or height data, or having only one dietary recall. Based on our previously published methods, a physiologically plausible reported energy intake was calculated as being within +/-22% of predicted energy requirements for the mean of two 24-hour recalls. RESULTS: Reporting plausibility ([reported energy intake/predicted energy requirements]x100) averaged 83% in the total sample (N=4,539) and increased to 96% in the plausible sample (n=1,932). Only approximately 5% of the plausible sample consumed the Adequate Intake for fiber. In plausibly reporting women, fiber, its interaction with percentage energy from fat, and energy density were independently associated with BMI. Only percentage energy from fat was associated with BMI in men reporting plausibly. Compared with the total sample, stronger relationships between diet and BMI were observed among the plausible reporters. In women, a low-fiber (< 1.5 g/MJ), high-fat (> or = 35% energy) diet was associated with the greatest increase in risk of overweight or obesity compared with a high-fiber, low-fat diet. CONCLUSIONS: Weight control advice for US women should place greater emphasis on consumption of fiber.     

Dietary fiber and breast cancer

Evidence from epidemiological studies suggests that dietary fiber, as well as fat, has the potential for affecting breast cancer risk. Fiber may have a protective role because of its influence on estrogen metabolism and excretion or because of the endocrine effects of the lignans, a family of compounds formed in the intestine from fiber-associated precursors. Future research should include additional mechanistic studies and dietary intervention trials in groups of women that have a high risk of breast cancer.