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Probiotics and Bacteria: A Balancing Act
Probiotics may help to keep bacteria in check, and manage diarrhea and irritable bowel syndrome. Learn more about them and how they work.

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Picture of probiotics and pills Probiotics and Bacteria: A Balancing Act

Are probiotics the answer to intestinal ills? These "friendly" bacteria may play a role in digestive health. Studies show probiotics can help in treating some types of diarrhea and some symptoms of irritable bowel syndrome. They may also be useful for managing inflammation after colon removal.

Bacteria and your intestines
Your intestines contain a mix of bacteria and other microbes. You may hear them referred to as good and bad, or "friendly" and "unfriendly" bacteria. The exact mix of bacteria in your gut is set at birth. This balance, unique for each person, tends to stay the same throughout your life.

Friendly bacteria enhance your health by:

  • Strengthening the immune system
  • Keeping "unfriendly" bacteria in check
  • Helping you digest food and absorb nutrients

The healthy bacteria balance can be upset, though, by:

  • Antibiotics, which destroy the good bacteria along with the bad
  • Disease-causing bacteria, viruses, yeasts, fungi, or parasites

This is where probiotics can help when added to foods or when used as a supplement. These living microbes mimic the friendly bacteria and yeasts that exist naturally in your body. By adding more, you can increase the number of friendly bacteria to regain proper balance in your intestines.

Do probiotics really work?
In addition to keeping the bacteria balance optimal, there is good evidence that using probiotics may:

  • Reduce the incidence of diarrhea from antibiotic use
  • Reduce the ill effects of diarrhea caused by a virus
  • Reduce the extent of pain and bloating in some people with irritable bowels
  • Manage symptoms of pouchitis, a common inflammation after partial colon removal

Early evidence suggests that probiotics may also be helpful in treating vaginal yeast infections, bacterial stomach infections, bowel disease, and upper lung infections. More limited evidence suggests that probiotics may help in treating urinary tract infections and asthma, and in preventing colon cancer. However, more research is needed to support these claims.

Shopping for probiotics
Probiotics can be taken as capsules, powder, tablets, or liquid. They may also be added to cereals, yogurts, soy products, juices, and even baby formulas. But read labels closely to make sure you get the right amount. Not all foods with added probiotics have enough to be effective.

Here is what to look for:

Many product shave a mix of probiotic types. Look for one or more of these strains on the label:

  • Lactobacillus
  • Bifidobacterium
  • Streptococcus thermophilus
  • Saccharomyces boulardi.

The amount of probiotics in a supplement or food varies greatly. Most strains are measured in colony-forming units (CFU's), except for S. boulardii, which is measured in milligrams (mg).

  • Most studies use doses from 1 to 20 billion CFU's per day.
  • 5 to 10 billion CFU's per day in children and 10 to 20 billion CFU's per day in adults are common dosage ranges. For S. boulardii, the amount is 250 to 500 mg per day.
  • There is no data that higher doses are unsafe, but they may not be of use.

Are probiotics safe?
Probiotics are regulated as dietary supplements - not drugs - by the U.S. Food and Drug Administration. They appear to be safe for most healthy adults and children. Mild side effects, such as gas and bloating, are possible.

There have been rare reports of infection in adults with severe illnesses, chronic conditions like diabetes, or weak immune systems. Children with short-gut syndrome also have a higher infection risk.

Always check with your doctor before you try to add probiotics to your diet. Ask your doctor about reliable brands and dosage advice, too.

By Jane Schwartz Harrison, RD, Staff Nutritionist
Created on 03/17/2008
Updated on 06/16/2011
  • American Academy of Microbiology. Probiotic microbes: the scientific basis.
  • Turroni S, Vitali B, Candela M, et al. Antibiotics and probiotics in chronic pouchitis: a comparative proteomic approach. World Journal of Gastroenterology. 2010;16(1):30-41.
  • Allen SJ, Martinez EG, Gregorio GV, Dans LF. Probiotics for treating acute infectious diarrhoea. Cochrane Reviews. 2010;11.
  • National Center for Complementary and Alternative Medicine. Get the facts: An introduction to probiotics.
  • Kliger B, Cohrssen A. Probiotics. American Family Physician. 2008;78(9):1073-1078.
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