Dietary Recommendations For Fiber

The American Heart Association Eating Plan suggests eating a variety of food fiber sources. Fiber is important for the health of the digestive system and for lowering cholesterol. Foods containing fiber are good sources of other essential nutrients. Depending on how they're prepared, these foods are typically also low in fat, saturated fat and cholesterol. Fruits, vegetables, whole-grain and fortified foods, beans and legumes are good sources of both soluble and insoluble dietary fiber.

Total dietary fiber intake should be 25-30 grams a day. Right now dietary fiber intakes among adults in the United States average about 10-15 grams. That's about half the recommended amount.

What is dietary fiber?

Dietary fiber is the term for several materials that make up the parts of plants your body can't digest. Fiber is classified as soluble or insoluble.

When eaten regularly as part of a low-fat, low-cholesterol diet, soluble fiber has been shown to help lower blood cholesterol. Oats have the highest proportion of soluble fiber of any grain. Foods high in soluble fiber include oat bran, oatmeal, beans, peas, rice bran, barley, citrus fruits, strawberries and apple pulp. NOTE: Many commercial oat bran and wheat bran products (muffins, chips, waffles) actually contain very little bran. They also may be high in sodium, total fat and saturated fat. Read the labels carefully.

Insoluble fiber doesn't seem to help lower blood cholesterol. However, it's an important aid in normal bowel function. Foods high in insoluble fiber include whole-wheat breads, wheat cereals, wheat bran, rye, rice, barley, most other grains, cabbage, beets, carrots, Brussels sprouts, turnips, cauliflower and apple skin.

Fiber is also thought to reduce cancer risk by binding carcinogens in the intestines and making a favorable environment for beneficial bacterial flora. Fiber is acted upon by intestinal enzymes and microbes, yielding short chain fatty acids (SCFAs), which are noted to have anticancer effects. [1].

Fiber may also prevent gallstone formation. Dietary fiber appears to deter the synthesis and absorption of secondary bile acids (SBAs), which are unhealthy bile metabolites that form in the intestinal tract. Certain SBAs have been linked with increased cholesterol saturation of bile and thus gallstone formation. Fiber not only allows less time for SBAs to form in the gut by improving intestinal motility, it may also bind SBAs and escort them out of the body. Population research has confirmed that low-fiber diets predispose toward gallstone formation. [2].

Fiber's impact on Hypercholesterolemia

Fifty-one healthy, moderately hypercholesterolemic men and women consuming their usual fat-modified diets completed a 6-month, randomized, double-blind, placebo-controlled, parallel comparison of 15 g/day supplemental water-soluble dietary fiber (WSDF; a mixture of psyllium, pectin, guar gum, and locust bean gum) and an inactive WSDF control (acacia gum). The WSDF mixture yielded 6.4% and 10.5% reductions in mean plasma total and low-density lipoprotein cholesterol concentrations, respectively, after 8 weeks, which were sustained at 16 and 24 weeks. [3].

Water-soluble dietary fibers (WSDF) are generally thought to lower cholesterol. Another study compared the cholesterol-lowering effects of a medium viscosity WSDF mixture (psyllium, pectin, guar gum and locust bean gum) with an equal amount of WSDF from acacia gum, which has a lower viscosity. Hypercholesterolemic males (n = 13) and females (n = 16) were randomly assigned to one of two WSDF treatments provided in a low-calorie powder form for mixing into beverages.

WSDF mixture yielded a 10% decrease in plasma total cholesterol (from 251 +/- 20 to 225 +/- 19 mg/dL; p < 0.01), and a 14% reduction in low-density lipoprotein cholesterol (from 167 +/- 14 to 144 +/- 14 mg/dL; p < 0.001). In contrast, the acacia gum-treated group showed no change in any plasma lipid parameters. These data support previous findings that a diet rich in select WSDF can be a useful cholesterol-lowering adjunct to a fat-modified diet, but that caution should be exercised in ascribing cholesterol-lowering efficacy to dietary fibers based solely on their WSDF classification. [4].

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