Monday, June 10, 2013

Learning Nutrition: Dietary Fiber

By Allyn Luong


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.

According to the recommendations, a typical American man ought to consume 30 to 38 grams of dietary fiber per day while a woman should consume between 21 to 25 grams of fiber per day. However, the actual intake of dietary fiber is much lower than suggested. It is believed that women are consuming only 13 grams and men's consumption is only 17 grams of 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.

Major studies have shown that higher fiber consumption, especially water soluble fiber, is associated with a decline in coronary heart disease risk. An investigation of ten studies detected a 12% fall in the risk for coronary events and a 19% decline in the risk of death for each 10 g increase in dietary fiber per day.

The National Cholesterol Education Program recommends an ingestion of 5 to 10 g of soluble fiber daily to improve LDL-C (low density lipoprotein) levels. The American Heart Association (AHA) endorses a total dietary fiber intake of 25 to 30 g/d from foods, not supplements, to ensure nutrient balance 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 intake could interfere with the absorption of minerals, such as iron, zinc, magnesium, and calcium.




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