Does Fiber Inhibit the Absorption of Nutrients?

Ripe raspberries on a plant.
Raspberries and other berries are rich in soluble fiber. (Image: FrankCornfield/iStock/Getty Images)

You're probably aware that dietary fiber is generally healthy, helping move food through your digestive tract and possibly preventing constipation and other problems. But a type called soluble fiber can also inhibit your body's absorption of nutrients such as carbohydrates and fat, an effect that could have significant health benefits, including lowering your risk of chronic disorders.

Carbohydrate Absorption

Two types of fiber exist, insoluble and soluble. While both are healthy, soluble fiber forms a gel when mixed with fluid in your stomach, preventing rapid uptake of carbohydrates, such as starch and sugar. Research suggests that this can help prevent large increases in blood glucose after a meal, an effect that might lower your risk of developing Type 2 diabetes. In one clinical trial published in the April 2010 issue of the "Journal of Nutrition," healthy adults who consumed a soluble fiber supplement had lower post-meal levels of blood glucose and insulin, the hormone that lowers blood sugar, compared to a placebo group. According to the University of Maryland Medical Center, other research indicates that people with Type 2 diabetes who eat lots of soluble fiber also tend to have lower blood glucose levels.

Effects on Fat

Eating a diet rich in soluble fiber can also slow uptake of dietary fats into your blood, according to the University of Maryland Medical Center. When combined with a low-fat diet, fiber can help lower your blood levels of cholesterol and reduce your risk of cardiovascular problems. Research such as a study published in the February 2000 issue of the "American Journal of Clinical Nutrition" supports this benefit of a diet high in soluble fiber. Researchers examined results of eight clinical trials involving more than 600 subjects with high cholesterol who consumed soluble-fiber supplements or a placebo. In all eight trials, subjects in the high-fiber group had significantly lower levels of total blood cholesterol and low-density lipoprotein, or "bad" cholesterol, compared to the placebo group.

Other Nutrients

A healthy diet is also rich in vitamins, minerals and healthy phytonutrients. Although most of these nutrients are unaffected by fiber consumption, you might absorb less beta carotene, lycopene and lutein, three phytonutrients found in certain vegetables and fruits, if you combine these with foods high in soluble fiber, according to the Linus Pauling Institute. The 2010 Dietary Guidelines for Americans recommend that a woman consume at least 25 and a man at least 38 grams of dietary fiber daily. If your consumption is in this range and you take in less than 40 grams of fiber daily, it won't interfere with absorption of other essential nutrients such as calcium, magnesium or zinc, but you should add fiber gradually to prevent gastric distress or bloating.

Sources of Soluble Fiber

Most fruits, vegetables and whole-grain foods are rich in fiber, but some types are especially good sources of soluble fiber. For example, 1/2-cup serving of Brussels sprouts, turnips, black beans or sweet potatoes provides between 2 and 2.4 grams of soluble fiber, while the same amount of beets, carrots and broccoli provide about 1 gram. Fruits that are high in soluble fiber include oranges and fresh apricots, with about 2 grams in four apricots or one orange; raspberries, which have about 1 gram per cup; and strawberries, which have about 1 gram per 1 1/4-cup serving. You can also increase your intake of soluble fiber by taking supplements containing psyllium husks, but discuss their use with your doctor or a registered dietitian to decide what's best for you.

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