What are probiotics?
Probiotics are bacteria that help maintain the natural
balance of organisms (microflora) in the
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 proven which probiotics (alone or in combination) work
to treat diseases. At this point, even the strains of probiotics that
have been proven to work for a specific disease are not widely
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 development of
other infections, such as vaginal yeast and
urinary tract infections, and symptoms such as diarrhea from
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 medication. 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
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