There are two absorption systems in your body. Food that is easily broken down is absorbed into your upper intestinal tract. If you cannot absorb a particular food, it goes to the lower intestinal tract (colon), where bacteria (in your colon) ferment it to smaller products that can be absorbed.

Your colon is loaded with good and bad bacteria. Examples of bad bacteria are clostridia that are kept in check by good bacteria. If you take an antibiotic that knocks off the good bacteria, the clostridia can overgrow and cause horrible bloody diarrhea and you can die if you are not given special antibiotics, specific to kill clostridia, such as metronidazole and vancomycin.

The good bacteria break down soluble fiber to form chemicals such as short chain fatty acids that are absorbed into your bloodstream and travel to your liver where they block the liver from making cholesterol and help to prevent heart attacks. These short chain fatty acids also reduce inflammation, so they help to control the horrible bloody diarrhea and ulcers caused by Crohn's disease. They also reduce swelling and pain of arthritis, diabetes and psoriasis, and some studies show they may even improve your immunity to help you to kill germs.

One example of friendly bacteria is lactobacilli, found in live-culture yogurt. However, lactobacilli do not thrive in your intestines and disappear if you don't eat yogurt every day. Most commercial yogurts do not contain live cultures; check the labels if you seek this benefit.

Foods that cannot be absorbed in your upper intestinal tract pass to your colon and form the food for the huge colony of friendly bacteria there. These include whole grains, beans, seeds, vegetables and nuts. The part of these foods that encourages the growth of good bacteria is most likely the soluble fiber.

So probiotics are living microorganisms, the good bacteria, that live in the colon and reduce inflammation and help prevent and treat Crohn's disease, psoriasis, arthritis, and perhaps even certain types of cancers.

Prebiotics are the nondigestible food ingredients that cannot be absorbed in the upper intestinal tract and travel to the colon to encourage the growth of these good bacteria. A healthful, high-fiber diet will include a wide variety of these foods.

Dr. Gabe Mirkin has been a radio talk show host for 25 years and practicing physician for more than 40 years; he is board certified in four specialties, including sports medicine. Read or listen to hundreds of his fitness and health reports at http://www.DrMirkin.com

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