Dietary Fiber: The Basics
Fiber is an essential component of our diets, yet most Americans don’t eat enough, with usual intakes of approximately half the daily recommendation.1
Article By: The Weight Watchers Research Department
Because fiber is found primarily in the cell walls of plants, plant-based foods – whole grains, legumes, vegetables, fruits, and nuts – are major food sources. Fiber also is supplied by a variety of processed foods that have been modified with added fiber.
Defining Fiber: Modern Terms
The term “dietary fiber" primarily describes long-chain carbohydrates whose bonds cannot be broken down by digestive enzymes in the small intestine. Included in this definition is resistant starch, a non-digestible starch found in legumes and some vegetables, as well as in resistant starch food products. Non-digestible carbohydrates reach the large intestine, where many are metabolized by colonic bacteria.
Fiber historically has been classified as soluble or insoluble, although in 2002 the Institute of Medicine (IOM) recommended new classifications – “dietary fiber", the fiber naturally occurring in foods, and “functional fiber", namely those fibers that have been isolated, modified or manufactured for a specific purpose or health benefit.1 The listing of Dietary Fiber on the Nutrition Facts panel represents the total of all types of fibers in the food.
Health Benefits of Fiber
The health benefits of a high fiber diet extend beyond its traditional association with improved laxation and overall digestive health.2 In a landmark study of more than 9,000 participants in the National Health and Nutrition Examination Survey (NHANES), those whose diet was highest in fiber were less likely to develop heart disease. Furthermore, a pooled analysis of 10 prospective studies found that diets high in dietary fiber were associated with lower risk of heart disease and death from heart disease. In fact, evidence of this inverse relationship between fiber and heart disease is strong enough to support two FDA- approved health claims. Data also support the importance of fiber for helping to regulate blood glucose, preventing and/or treating gastrointestinal disorders and reducing risk for certain types of cancer.5
Fiber may also benefit weight management in several ways. Fiber-rich foods can help with hunger management by boosting feelings of fullness. Studies show that increasing fiber is associated with cutting calories and that people who eat the most fiber have a lower Body Mass Index (BMI).
Recommended Intake
The 2010 Dietary Guidelines for Americans recommend a fiber intake of 14 g per 1,000 calories, or 25 g per day for women and 38 g per day for men. To meet this recommendation, the Guidelines suggest including beans and peas (legumes), other vegetables, fruits, whole grains, and other foods with naturally occurring fiber. Foods labeled “good source of fiber" contain at least 10 percent of the recommended amount or 2.5 g/serving and those labeled “excellent source of fiber" contain at least 20 percent of the recommended amount (≥5 g/serving).
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1 Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes: Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids. Washington, DC: National Academies Press; 2002.
2 Slavin, JL. Position of the American Dietetic Association: health implications of dietary fiber.. J Am Diet Assoc, 2008;108:1716-31.
3 Bazzano LA, He J, Ogden LG, et al. Dietary fiber intake and reduced risk of coronary heart disease in US men and women: the National Health and Nutrition Examination Survey I Epidemiologic Follow-up Study. Arch Intern Med. 2003;163:1897-1904.
4 Pereira MA, O’Reilly E, Augustsson K, et as. Dietary fiber and risk of coronary heart disease: a pooled analysis of cohort studies. Arch Intern Med. 2004;164:370-376.
5 Howarth NC, Saltzman E, Roberts SB. Dietary fiber and weight regulation. Nutr Rev. 2001;59:129-39.
6 Liu S, Willett WC, Manson JE, et al. 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;87:920-927.
7 U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th Edition, Washington, DC: U.S. Government Printing Office, December 2010.