All fibers are not created equal

Posted on May 9, 2009. Filed under: cholesterol, diabetes, inulin, nutrition, oat bran, obesity, psyllium, resistant starch, weight |

Dietary fiber consumption has many health benefits. Persons who have the highest intakes of whole grains are significantly less likely to develop heart attacks, strokes, diabetes, obesity, high blood pressure, gastrointestinal disorders, and certain forms of cancer (Anderson JW, Nutrition Reviews, Apr. 2009). Currently scientists are actively testing various types of fiber to discern which types of fibers contribute to these health benefits.

Wheat bran was popularized by the late Dr. Denis Burkitt, a friend and mentor. Wheat bran has a major benefit for regularity—it keeps things moving. It also may lower blood pressure slightly and probably contributes to weight management. However, it does not lower blood cholesterol or smooth out the blood sugar after a meal. Oat bran is the most versatile type of fiber in that it has all the health benefits currently attributed to dietary fiber, namely: improves laxation, lowers blood cholesterol, lowers the blood glucose rise after meals (glycemic effects), lowers blood pressure, assists in weight loss and management, and is a prebiotic that enhances immune function. (I was called Dr. Oat Bran during the 1980’s, the Oat Bran Decade).

Psyllium is the most potent fiber supplement in that it improves laxation, lowers blood cholesterol, lowers the blood glucose rise after meals (glycemic effects), lowers blood pressure, and assists in weight loss and management. Psyllium does not appear to be a prebiotic or enhance immune function.

Many viscous, soluble fibers such as oat and barley gum, guar gum, pectins and konjac mannan have these benefits: lowers blood cholesterol, lowers the blood glucose rise after meals (glycemic effects), and assists in weight loss and management. Some of these fibers such as oat and barley gum (B-glucans) are prebiotics and enhance immune function.

Inulins and resistant starches are fairly new members of the fiber family. Inulin and similar carbohydrates are clearly prebiotics and enhance immune function. The other health benefits of inulin are uncertain but it does not appear to lower blood cholesterol.

Resistant starches include a wide variety of starches in foods and starches that are modified to make them resistant to the action of digestive enzymes in the small intestine. These starches are not digested but travel to the colon where they are completely fermented by bacteria. While most are fermented, like inulin, most are not prebiotics and do not enhance immune function. Further work is required in this area. The main benefit of the resistant starches is that they lower the blood glucose increase after a meal (glycemic effect). None of the resistant starches have been approved to make a claim that they have laxation benefits.

Thus, all fibers are not created equal and the consumer must decide what health benefits are most important. Currently oat bran foods and psyllium supplements appear to provide the widest range of health benefits.

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One Response to “All fibers are not created equal”

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You’re absolutely right that all fibers are not equal. You’ve missed some of the important benefits shown with natural resistant starch – improved insulin sensitivity and increased satiety. The fermentation of natural resistant starch in the large intestine has been shown to turn on the genes that make satiety hormones GLP-1 and PYY, and these hormones have stayed high for 20+ hours. Another fiber in the study showed no effect at all. We’re not used to thinking about foods helping us eat less the next day, but that’s what it appears that natural resistant starch does. You’ve also missed 6 human clinical trials have shown that natural resistant starch from high amylose corn improves laxation and other aspects of digestive health. The newer, chemically modified forms of resistant starch have very little or no evidence of efficacy, but natural resistant starch from high amylose corn is supported by 70 clinical studies.

Psyllium and oat bran may help people lower cholesterol, but how many other dietary ingredients actively help you to eat less or increase insulin sensitivity directly?


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