Learning About Dietary Fiber

By Litia Niedewski

Learning About Dietary Fiber

Dietary fibers are a portion of plants that are resistant to digestion. They are complex carbohydrates, classified based on their solubility in fluids. Soluble fibers (pectins, gums, mucilages) dissolve in fluids, and influence the absorption of glucose, lipids and other nutrients. Insoluble fibers (cellulose, hemicellulose, and lignin), which are not soluble in fluids, contribute more to an increased stool weight and reduced intestinal transit time.

Based on the guidelines, a regular American man should consume 30 to 38 grams of fiber daily while a woman should consume between 21 to 25 grams of dietary fiber per day. But the actual intake of dietary fiber is much worse than recommended. It is assumed that women are consuming only 13 grams and men's intake is just 17 grams of dietary fiber per day.

Researchers believe that soluble fibers form a gel in the stomach leading to sluggish gastric emptying and a higher rate of absorption of the nutrients. This increases satiety and leads to lower food intake which is reflected in reduced weight gain. Moreover, fermentation of fiber in the large intestine leads to reactions which finally reduce the serum cholesterol levels.

Large studies have shown that increased fiber intake, especially water soluble fiber, is associated with a decrease in coronary heart disease risk. An analysis of ten studies detected a 12% reduction in the risk for coronary events and a 19% reduction in the risk of death for each 10 g increment in dietary fiber per day.

The National Cholesterol Education Program (NCEP) recommends an intake of 5 to 10 g of soluble fiber per day to improve LDL-C (low density lipoprotein) blood levels. The American Heart Association recommends a total dietary fiber intake of 25 to 30 g/d from diets, not supplements, to ensure nutrient adequacy and to maximize the cholesterol-lowering impact of a fat-modified diet.

Many studies have revealed that a greater fiber intake could reduce systemic blood pressure. One study indicated that the effects of fiber consumption were more distinct in older compared to younger patients. High fiber intake could also reduce blood cholesterol levels.

Fiber consumption could cause increased bloating. However, the severity of the side effects is limited when fiber intake is reduced. Fibers that are less fermented, such as psyllium, may also help in this regard. Drinking sufficient amounts of fluid and slowly increasing the amount of fiber intake could also limit bloating.

High fiber consumption could interfere with the absorption of minerals, such as iron, zinc, magnesium, and calcium.


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