Fiber is a carbohydrate component of plant foods that is not absorbed in the body. A diet with enough fiber can succeed because of the way fiber acts in the body; promoting fullness and bowel regularity. Including fiber in the diet can also help lower cholesterol. Choosing foods with low calories and high fiber content is key to maintaining a healthy lifestyle.
Fiber Requirements
Because a sufficient fiber intake for healthy individuals, or RDA, has not been determined, fiber has an Adequate Intake level. This is the level considered to be an adequate intake of fiber. According to the USDA's Dietary Guidelines for Americans in 2010, the AI for fiber is 14 g per 1,000 calories. The average American, however, does not consume this much fiber.
Soluble Fiber
Soluble fiber is also known as viscous fiber. This fiber delays gastric emptying, so it slows down absorption of nutrients in the small intestine. The slow emptying and absorption allow the energy from foods to be released slowly. An increased soluble fiber intake, therefore, can aid in weight management. Soluble fiber can also help lower blood cholesterol levels. Soluble fiber binds with bile acids in the body that contain cholesterol, increasing cholesterol excretion. Bacteria left in the colon after fiber fermentation can inhibit cholesterol synthesis in the liver, also resulting in lower blood cholesterol levels.
Insoluble Fiber
Insoluble fiber, or non-viscous fiber, is important for increasing fecal bulk and speeding its passage through the colon. This promotes bowel regularity and helps to prevent constipation. Insoluble fiber also lowers the risk of health problems like diverticulosis and hemorrhoids by easing bowel movements. The bulk that insoluble fiber provides may also aid in weight management. It does so by promoting feelings of fullness, reducing the likelihood of overeating.
Foods High in Fiber
Foods high in soluble fiber include citrus fruits, apples, prunes, legumes, oatmeal and oat bran. Foods high in insoluble fiber include many vegetables that are leafy and green, fruit skins, whole grain breads and pastas, wheat bran and seeds and nuts.
References
- The Mayo Clinic Diet; Mayo Clinic; 2010
- Nutrition Second Edition; Insel, Turner, Ross; 2004
- Dietary Reference Intakes; Institute of Medicine; 2006
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