There are two types of fiber: soluble and insoluble. Both soluble and insoluble fibers are undigested, meaning they are not absorbed into the bloodstream. Soluble fiber is "soluble" in water; when mixed with water, it forms a gel-like substance and swells.
Insoluble fiber does not absorb or dissolve in water; it passes through our digestive system in close to its original form. Insoluble fiber offers many benefits to intestinal health, including a reduction in the risk and occurrence of colorectal cancer, hemorrhoids, and constipation. Cellulose and lignins are two insoluble fibers. Among the advantages of eating insoluble fiber is its ability to increase bulk and therefore soften stools and shorten transit time through the GI tract.
Due to the overlap in function between the two types of fiber and the difficulty in measuring each type, the National Academy of Sciences is recommending that the terms soluble and Insoluble gradually be eliminated and replaced by specific beneficial effects of each fiber. Thus, you may hear less about soluble vs. insoluble fiber in the future.
Plant foods contain both types of fiber in varying degrees, according to the plant's characteristics. Examples of foods rich in soluble fiber are fruits, vegetables, brown rice, barley, and nuts. Most of insoluble fibers come from the bran layers of cereal grains. Examples of foods rich in insoluble fiber are wheat bran and whole-grain breads and cereals. Remember, both are important for good health, so your diet should include a balance of foods rich in both types.
There is no RDA for fiber, but the American Dietetic Association recommends eating 20-35 grams of dietary fiber per day or 10-13 grams for every 1,000 calories in the diet. The average American significantly falls short of the recommended amount of fiber, consuming on average only 5-10 grams per day.
Here are some easy suggestions for how patients can increase their fiber intake:
- Choose whole fruits and vegetables (with peels when possible) instead of juices.
- Replace white flour with whole wheat flour in all baked goods.
- Select whole-grain bread, pasta and cereals in place of similar processed versions.
- Choose brown rice over white rice.
- Replace meat with alternate protein sources such as beans, lentils or other legumes.
Dr. Donald L. Hayes, DC is a clinician, educator and author of several books, including Lifestyle Wellness and, along with Michael E. Gerber, The E-Myth Nutritionist: Why Most Healthcare Practices Don't Work and What to Do About It. He is founder and president of the Greens First line of nutritional products and the Lifestyle Wellness Total Health Improvement Program. He can be reached at 866-410-1818 or through www.greensfirst.com.