What are probiotics?
Probiotics are bacteria that help maintain the natural balance of organisms (microflora) in the intestines. The normal human digestive tract contains about 400 types of probiotic bacteria that reduce the growth of harmful bacteria and promote a healthy digestive system. The largest group of probiotic bacteria in the intestine is lactic acid bacteria, of which Lactobacillus acidophilus, found in yogurt, is the best known. Yeast is also a probiotic substance. Probiotics are also available as dietary supplements.
It has been suggested that probiotics be used to treat problems in the stomach and intestines. But only certain types of bacteria or yeast (called strains) have been shown to work in the digestive tract. It still needs to be proved which probiotics (alone or in combination) work to treat diseases. At this point, even the strains of probiotics that have been proved to work for a specific disease are not widely available.
What are probiotics used for?
In most circumstances, people use probiotics to prevent diarrhea caused by antibiotics. Antibiotics kill "good" (beneficial) bacteria along with the bacteria that cause illness. A decrease in beneficial bacteria may lead to diarrhea. Taking probiotic supplements (as capsules, powder, or liquid extract) may help replace the lost beneficial bacteria and thus help prevent diarrhea.
A decrease in beneficial bacteria may also lead to other infections, such as vaginal yeast and urinary tract infections, and symptoms such as diarrhea from intestinal illnesses.
Research has shown that certain probiotics may restore normal bowel function and may help reduce:1
- Diarrhea that is a side effect of antibiotics.
- Certain types of infectious diarrhea.
- Inflammation of the ileal pouch (pouchitis) that may occur in people who have had surgery to remove the colon.
These results suggest that eventually probiotics may also be used to:
- Help with other causes of diarrhea.
- Help prevent infections in the digestive tract.
- Help control immune response (inflammation), as in inflammatory bowel disease (IBD).
Researchers are studying the use of probiotics for inflammatory bowel disease, colon cancer, and irritable bowel syndrome (IBS).
The results of some early studies suggest that probiotics found in yogurt may help prevent diarrhea caused by antibiotics.1 But more studies are needed to confirm that yogurt is effective. To offer benefit, the yogurt must contain active cultures. Most yogurt containers indicate whether active cultures are present.
Are probiotics safe?
Probiotic bacteria are already part of the normal digestive system and are considered safe.
The U.S. Food and Drug Administration (FDA) does not regulate dietary supplements in the same way it regulates medicines. A dietary supplement can be sold with limited or no research on how well it works or on its safety.
Always tell your doctor if you are using a dietary supplement or if you are thinking about combining a dietary supplement with your conventional medical treatment. It may not be safe to forgo your conventional medical treatment and rely only on a dietary supplement. This is especially important for women who are pregnant or breast-feeding.
When using dietary supplements, keep in mind the following:
- Like conventional medicines, dietary supplements may cause side effects, trigger allergic reactions, or interact with prescription and nonprescription medicines or other supplements you are taking. A side effect or interaction with another medicine or supplement may make other health conditions worse.
- Dietary supplements may not be standardized in their manufacturing. This means that how well they work or any side effects they cause may differ among brands or even within different lots of the same brand. The form you buy in health food or grocery stores may not be the same as the form used in research.
- The long-term effects of most dietary supplements, other than vitamins and minerals, are not known. Many dietary supplements are not used long-term.
Last Updated: June 30, 2009
Author: Eileen Ellig & Jeannette Curtis