by Dr. Leo Galland
Fiber is the name given to complex carbohydrates that are resistant to human digestion. Examples of fiber include cellulose and pectin. Fiber comes from plants, and the usual sources are vegetables, cereals, bread, nuts, seeds and fruit.
Medical researchers have been recommending high fiber diets, yet dietary patterns in North America show no significant increase in fiber consumption from food. This means that the fiber intake of most people is far below recommended levels.
Soluble fiber from food sources, for example from apples, produces short chain fatty acids (SCFAs) in the intestine. SCFAs have a number of positive effects on the body: they nourish the cells of the large intestine, stimulating healing. When absorbed from the intestine, they travel to the liver and can decrease the liver’s production of cholesterol, lowering cholesterol levels. That’s why eating oat bran, which contains fibers of moderate solubility can lower cholesterol levels. Within the intestinal canal, SCFAs can inhibit the growth of yeast and disease-causing bacteria.
Fiber may also help increase longevity and protect against the development of parasitic infection. Excellent sources of mixed fibers are unrefined cereal grains (oats, brown rice, whole wheat), peas, beans and squash.
Among fruits, one gets the most fiber per serving from apples and berries.
Research Abstracts on Dietary Fiber:
Nutr Rev. 2009 Apr;67(4):188-205. Health benefits of dietary fiber.
Anderson JW, Baird P, Davis RH Jr, Ferreri S, Knudtson M, Koraym A, Waters V, Williams CL. Department of Internal Medicine and Nutritional Sciences Program, University of Kentucky, Lexington, Kentucky 40502, USA. firstname.lastname@example.org
Dietary fiber intake provides many health benefits. However, average fiber intakes for US children and adults are less than half of the recommended levels. Individuals with high intakes of dietary fiber appear to be at significantly lower risk for developing coronary heart disease, stroke, hypertension, diabetes, obesity, and certain gastrointestinal diseases. Increasing fiber intake lowers blood pressure and serum cholesterol levels. Increased intake of soluble fiber improves glycemia and insulin sensitivity in non-diabetic and diabetic individuals. Fiber supplementation in obese individuals significantly enhances weight loss. Increased fiber intake benefits a number of gastrointestinal disorders including the following: gastroesophageal reflux disease, duodenal ulcer, diverticulitis, constipation, and hemorrhoids. Prebiotic fibers appear to enhance immune function. Dietary fiber intake provides similar benefits for children as for adults. The recommended dietary fiber intakes for children and adults are 14 g/1000 kcal. More effective communication and consumer education is required to enhance fiber consumption from foods or supplements.
J Am Diet Assoc. 2008 Oct;108(10):1716-31. Position of the American Dietetic Association: health implications of dietary fiber.
Slavin JL. American Dietetic Association, USA.
Erratum in: J Am Diet Assoc. 2009 Feb;109(2):350.
It is the position of the American Dietetic Association that the public should consume adequate amounts of dietary fiber from a variety of plant foods. Populations that consume more dietary fiber have less chronic disease. In addition, intake of dietary fiber has beneficial effects on risk factors for developing several chronic diseases. Dietary Reference Intakes recommend consumption of 14 g dietary fiber per 1,000 kcal, or 25 g for adult women and 38 g for adult men, based on epidemiologic studies showing protection against cardiovascular disease. Appropriate kinds and amounts of dietary fiber for children, the critically ill, and the very old are unknown. The Dietary Reference Intakes for fiber are based on recommended energy intake, not clinical fiber studies. Usual intake of dietary fiber in the United States is only 15 g/day. Although solubility of fiber was thought to determine physiological effect, more recent studies suggest other properties of fiber, perhaps fermentability or viscosity are important parameters. High-fiber diets provide bulk, are more satiating, and have been linked to lower body weights. Evidence that fiber decreases cancer is mixed and further research is needed. Healthy children and adults can achieve adequate dietary fiber intakes by increasing variety in daily food patterns. Dietary messages to increase consumption of high-fiber foods such as whole grains, legumes, fruits, and vegetables should be broadly supported by food and nutrition professionals. Consumers are also turning to fiber supplements and bulk laxatives as additional fiber sources. Few fiber supplements have been studied for physiological effectiveness, so the best advice is to consume fiber in foods. Look for physiological studies of effectiveness before selecting functional fibers in dietetics practice.
Crit Rev Food Sci Nutr. 2008 Nov;48(10):905-12.
Dietary fiber in the prevention and treatment of metabolic syndrome: a review.
Aleixandre A, Miguel M. Department of Pharmacology, Faculty of Medicine, Complutense University, Madrid, Spain.
Inclusion of fiber in the diet has been linked to the prevention of a range of illnesses and conditions. This review contains several ideas about the possible benefits of dietary fiber intake in patients with metabolic syndrome. The principal beneficial effects of a fiber-rich diet in these patients are: prevention of obesity, improved glucose levels, and control of the profile of blood lipids. We now also know that dietary fiber may favor the control of arterial blood pressure. Animal experiments have also shown the benefit of different types of fiber on these variables. Of particular relevance are the studies using obese Zucker rats, which present similar anomalies to those seen in patients with metabolic syndrome. There is therefore a growing interest in discovering new sources of natural fiber. Some of these different kinds of fiber may then be used as functional ingredients to obtain foods with properties that are beneficial to health.