Fill Up on Fiber—Fight Fat?

Taking in loads of dietary fibers, which are found in natural foods like fruits, vegetables, legumes and whole grain cereals reduces the risk of diabetes and cardiovascular disease.¹ As an added bonus, epidemiologic studies provide evidence that high dietary fiber intake prevents obesity and is inversely related to body weight. For instance, one study of 2909 participants (CARDIA) looked at the relationship between dietary fiber intake and weight gain over ten years.¹ Participants with fiber intakes in the highest 1/5 of the study group had body weights that were significantly lower than those in the lowest 1/5 of fiber intake. Liu et al.² used data from The Nurses Health Study, a study of 74,091 nurses over time, to show that women who increased dietary fiber the most gained about 3.3lb fewer pounds than women with the smallest fiber increase over 12 years. Increasing dietary fiber intake may allow an individual to maintain his or her weight over time.

In 2009, Tucker and Thomas reported the effect of women’s dietary fiber intake on weight gain and fat gain over 20 months, while controlling for factors like age, body weight, fat intake, energy intake and physical activity³. The women were asked to keep a 7–day weighed food record at the beginning of the study and after 20 weeks. The investigators determined that for every 1g decrease of dietary fiber intake (per 1000 kcal) per day, the women gained about 0.5lb (P=0.0061) and increased their body fat by about 0.25% (P=0.0052). On the other hand for every 1g (per 1000 kcal) of increased fiber consumption, the women lost about 0.5lb. When the weight changes were analyzed while controlling for overall energy intake, the association between a decrease in fiber intake and weight gain weakened, but was still significant. The change in body fat % was not ssignificant after controlling for overall energy intake.

Lean and Obese People

The modulation of weight by fiber intake may be dependent upon the initial size of participants. In the 12 year evaluation of the Nurses Health Study, as conducted by Liu et al.², a 14g daily increase of daily fiber intake was associated with a reduction in weight gain of about 7.7lb over 12 years, on average. If the women were overweight at baseline, the reduction of weight gain was greater than in participants who were lean to begin with. In essence, high fiber intake may protect overweight participants from becoming obese. In fact, the risk of developing obesity was decreased by 50% for the women who increased their fiber intake to the highest 1/5 of the group.

In an analysis of 12 intervention studies Howarth et al.⁴ reported that an increase in dietary fiber intake of 14g/day is associated with a 4.2lb weight loss over 3.8 months. Furthermore, participants that were initially obese benefited from weight loss that was three times that of lean participants. These studies suggest that increasing dietary fiber, in addition to emphasis on Calorie intake and macronutrient composition may be very important an overweight or obese person tried to lose weight. Also, feeding kids a diet with sufficient dietary fiber may help to prevent excessive weight gain.^5,6

Functional (Supplemental) Vs. Dietary Fibers

Though fiber supplements are marketed as a healthful addition to weight-loss diets, does the evidence support that fiber supplements will yield the same benefits observed for long-term dietary fiber intake? Unfortunately, the research has not been thorough enough to examine whether fiber supplements are as good as mixed dietary sources of fiber. And as research of fiber intake and LDL lipids ("bad" cholesterol) has suggested, different sources of dietary fiber have differential effects in the human body.⁶ Therefore, the association between each type of supplemental fiber and weight loss would have to be examined before definitive conclusions may be made about fiber supplement and weight loss. On the other hand, some reviews suggestthat fiber supplement in the amount of 6-7g/day may aid weight loss efforts in combination with a hypocaloric diet.^7,8

How Does Fiber Work?

Many mechanisms have been suggested for how dietary fiber aids in weight management, including promoting satiation, decreasing absorption of calories, and altering secretion of gastrointestinal hormones, including ghrelin and CCK. Some researcher think that fiber helps with weight loss mostly through energy displacement (fiber bulk replaces foods with more calories in the diet), since the impacts of fiber intake on weight loss are much less when energy intake is controlled for statistically.

Conclusion

There is convincing evidence to suggest that increasing dietary fiber will reduce overall energy intake and promote weight loss or weight maintenance in overweight and obese individuals. Some studies show greater weight loss for people who receive a fiber supplement in combination with a low calorie diet^7,8—the bulk of added fiber may make it easier for someone to follow a lower Calorie diet plan. The best approach is probably to eat a diet high in natural fibers from primarily fruits, vegetable, legumes and whole grains and maybe add a daily fiber supplement in the amount of 7-14g/day. Experimentally, oat bran, inulin, psyllium and guar gum may be good supplemental fiber choices.

References

1. Ludwig DS, Pereira MA, Kroenke CH, Hilner JE, Van Horn L, Slattery ML, Jacobs DR Jr. Dietary fiber, weight gain and cardiovascular disease risk factors in young adults. JAMA. 1999;282:1539-1546.
2. Liu S, Willet WC, Manson JE, Hu FB, Rosner B, Colditz G. Relation between changes in intakes of dietary fiber and grain products and changes in weight and development of obesity among middle aged women. Am J Clin Nutr. 2003;78:920-927.
3. Tucker & Thomas. Increasing Total Fiber Intake Reduces Risk of Weight and Fat Gains in Women. J Nutrition, 2009; 139:1-6.
4. Howarth NC, Saltzman E, Roberts SB. Dietary fiber and weight regulation. Nutr Rev 2001;59:129-139.
5. Kimm SY. The role of dietary fiber in the development and treatment of childhood obesity. Pediatrics, 1995;96:1010-1014.
6. Erkkilä AT & Lichtenstein AH. Fiber and Cardiovascular Disease Risk: How Strong Is the Evidence? The Journal of Cardiovascular Nursing, 2006;21:3-8.
7. Editorial. Dietary Fiber and Control of Body Weight. Nutrition Metabolism and Cardiovascular Diseases, 2007;17:1-5.
8. Slavin JL. Dietary fiber and body weight. Nutrition, 2005;21:411-418.

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