- Increased dietary fiber consumption contributes to a number of unexpected metabolic effects independent from changes in body weight. This include improvement of insulin sensitivity, modulation of the secretion of certain gut hormones, and effects on various metabolic and inflammatory markers that are associated with the metabolic syndrome.1 Fiber also promotes weight loss by delaying the glucose absorption.
- High-fiber diets may protect against obesity and cardiovascular disease (CVD) by lowering insulin levels and blood pressure.2, 3 A large portion of the benefits of whole grain intake is attributed to dietary fiber.4, 5
- Increased dietary fiber consumption has a protective effect against CVD and its risk factors with a lower risk of developing coronary artery disease (CAD), stroke, high blood pressure, diabetes, obesity, and thereby reducing premature death in diverse populations.6-13
- A pooled analysis of 10 prospective cohort studies estimated that the risk of CVD death decreased by 19% for every 10g/day increase of dietary fiber intake.12 The recommended dietary fiber intakes for children and adults are 14g/1000 kcal or 25-30 g/day.
- Average fiber intake for US children and adults are less than half of the recommended levels.14 More effective communication and consumer education is required to enhance fiber consumption from foods or supplements.15
- The US Food and Drug Administration (FDA) approved health claims for two dietary fibers, beta-glucan (0.75 g/serving) and psyllium (1.78 g/serving), on the assumption that 4 servings/d would reduce CVD risk. A high-fiber diet containing beta-glucan or psyllium delivering 8 g/d more soluble fiber has been shown to have favorable effects on lipids and lipid ratios and reduce CVD risk by 4% compared to a control diet.16
- Whole grain cereals, legumes, oats, dark breads (such as wheat, rye, or pumpernickel), psyllium, and grapes are good sources of dietary fiber.
Nature and Types of Fiber
- Dietary fiber consists of edible parts of plants that are resistant to digestion and absorption in the human small intestine with partial or complete fermentation in the large intestine. Fiber can be classified as a dietary source (e.g., cereal, fruit, vegetable, or legume) or as a supplement.
- Based on chemical properties, fiber can be divided to water-soluble (e.g., beta-glucans, pectin, and guar) and insoluble (e.g., cellulose and lignin) forms.17
- Soluble fiber decreases LDL-C (low-density lipoprotein cholesterol) levels in the blood stream through increased production of cholesterol-binding bile acids which promote the excretion of lipids.17, 18 A mean reduction of 9% in LDL-C can be achieved by intake of different sources of soluble fiber.
- Incorporating fiber sources into our diet may provide a useful adjunct to a low-saturated fat diet, and especially in children and women of child bearing age who are hesitant or reluctant to take medications.19
- While soluble, gel-forming fiber has beneficial effects on CVD risk factors, insoluble fibers from whole grains have been most consistently associated with lower incidence rates of CVD. From a practical point of view a food-based approach favor increased intake of whole-grain cereals, fruit, and vegetables providing a mixture of different types of fibers for CVD prevention.17
- The physicochemical properties of soluble fiber result in important modifications in volume, bulk and viscosity in the intestinal lumen reducing transit time leading to better laxation, especially in the elderly.19
- Although both fruit and vegetable fiber have health benefits, insoluble cereal fiber in whole grains appears to have greater beneficial effects.20 The appropriate public health recommendation is to increase the consumption of whole grains at the expense of refined grains which would provide benefits not only from fiber, but also from other unique components of whole grains.1 Cereal fiber is an important source of magnesium.
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