How Does Dietary Fiber Work

By Josefina Gorenstein


Dietary fibers are a part of plants that are resilient to digestion. They are compound starches, classified based on their solubility in water. Solvable fibers (pectins, gums, mucilages) dissolve in water, and effect the absorption of sugar, fat and other nutrients. Insoluble fibers (cellulose, hemicellulose, and lignin), which are not solvable in fluids, contribute more to an greater stool weight and shorter transit time.


According to the guidelines, an average American man should consume 30 to 38 grams of dietary fiber per day while a woman should consume between 21 to 25 grams of dietary fiber per day. However, the actual intake of dietary fiber is much lower than recommended. It is thought that women are consuming only 13 grams and men's consumption is just 17 grams of dietary fiber per day.

Experts believe that soluble fibers form a gel in the stomach leading to sluggish gastric clearing and a higher rate of absorption of the nutrients. This increases satiety and leads to impaired food intake which is reflected in reduced weight gain. Additionally, fermentation of fiber in the large intestine leads to reactions which eventually reduce the blood cholesterol levels.

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

The National Cholesterol Education Program recommends an intake of 5 to 10 g of soluble fiber per day to improve LDL-C (low density lipoprotein) levels. The American Heart Association (AHA) recommends a total dietary fiber intake of 25 to 30 g/d from foods, 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 flatulence. Therefore, 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 adequate quantities of water and slowly increasing the amount of fiber intake could also limit bloating.

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




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