An Introduction to Probiotics
Probiotics are live microorganisms (in most cases, bacteria) that are similar to beneficial
microorganisms found in the human gut. They are also called "friendly bacteria" or "good
bacteria." Probiotics are available to consumers mainly in the form of dietary supplements and
foods. They can be used as complementary and alternative medicine (CAM), a group of diverse medical and health care systems,
practices, and products that are not presently considered to be part of conventional medicine. Complementary
medicine is used together with conventional medicine, and alternative medicine is used in place of conventional
medicine.. To find out more about topics and resources mentioned in this fact sheet, see "For More Information."
- People use probiotic products as CAM to prevent and treat certain illnesses and support general
- There is limited evidence supporting some uses of probiotics. Much more scientific knowledge is needed
about probiotics, including about their safety and appropriate use.
- Effects found from one species or strain of probiotics do not necessarily hold true for others, or even for
different preparations of the same species or strain.
- Tell your health care providers about any CAM practices you use. Give them a full picture of what you do to
manage your health. This will help ensure coordinated and safe care. For tips for talking with your health care
providers about CAM, see NCCAM's Time to Talk campaign.
Scanning electron micrograph (SEM) of Bifidobacterium bifidum.
Photo Credit: SciMAT/Photo Researchers, Inc
What Probiotics Are
Experts have debated how to define probiotics. One widely used definition, developed by the World Health
Organization and the Food and Agriculture Organization of the United Nations, is that probiotics are "live
microorganisms, which, when administered in adequate amounts, confer a health benefit on the host." (Microorganisms
are tiny living organisms—such as bacteria, viruses, and yeasts—that can be seen only under a microscope.)
Probiotics are not the same thing as prebiotics—nondigestible food ingredients that selectively stimulate the
growth and/or activity of beneficial microorganisms already in people's colons. When probiotics and prebiotics are
mixed together, they form a synbiotic.
Probiotics are available in foods and dietary supplements (for example, capsules,
tablets, and powders) and in some other forms as well. Examples of foods containing probiotics are yogurt,
fermented and unfermented milk, miso, tempeh, and some juices and soy beverages. In probiotic foods and
supplements, the bacteria may have been present originally or added during preparation.
Most probiotics are bacteria similar to those naturally found in people's guts, especially in those of breastfed
infants (who have natural protection against many diseases). Most often, the bacteria come from two
groups, Lactobacillus or Bifidobacterium. Within each group, there are
different species (for example, Lactobacillus acidophilus and Bifidobacterium bifidus), and within each species,
different strains (or varieties). A few common probiotics, such as Saccharomyces
boulardii, are yeasts, which are different from bacteria.
Some probiotic foods date back to ancient times, such as fermented foods and cultured milk products. Interest in
probiotics in general has been growing; Americans' spending on probiotic supplements, for example, nearly tripled
from 1994 to 2003.
Uses for Health Purposes
There are several reasons that people are interested in probiotics for health purposes.
First, the world is full of microorganisms (including bacteria), and so are people's bodies—in and on the skin, in
the gut, and in other orifices. Friendly bacteria are vital to proper development of the immune system, to
protection against microorganisms that could cause disease, and to the digestion and absorption of food and
nutrients. Each person's mix of bacteria varies. Interactions between a person and the microorganisms in his body,
and among the microorganisms themselves, can be crucial to the person's health and well-being.
This bacterial "balancing act" can be thrown off in two major ways:
- By antibiotics, when they kill friendly bacteria in the gut along with unfriendly bacteria. Some people use
probiotics to try to offset side effects from antibiotics like gas, cramping, or diarrhea. Similarly, some use
them to ease symptoms of lactose intolerance—a condition in which the gut lacks the enzyme needed to digest
significant amounts of the major sugar in milk, and which also causes gastrointestinal symptoms.
- "Unfriendly" microorganisms such as disease-causing bacteria, yeasts, fungi, and parasites can also upset
the balance. Researchers are exploring whether probiotics could halt these unfriendly agents in the first place
and/or suppress their growth and activity in conditions like:
- Infectious diarrhea
- Irritable bowel syndrome
- Inflammatory bowel disease (e.g., ulcerative colitis and Crohn's disease)
- Infection with Helicobacter pylori (H. pylori), a bacterium that causes most ulcers and many types of
chronic stomach inflammation
- Tooth decay and periodontal disease
- Vaginal infections
- Stomach and respiratory infections that children acquire in daycare
- Skin infections
Another part of the interest in probiotics stems from the fact there are cells in the digestive tract connected
with the immune system. One theory is that if you alter the microorganisms in a person's intestinal tract (as by
introducing probiotic bacteria), you can affect the immune system's defenses.
Color enhanced scanning electron micrograph (SEM) of the bacteria Lactobacillus acidophilus. A spirochete
bacteria can also be seen at center.
Photo Credit: SciMAT/Photo Researchers, Inc
What the Science Says
Scientific understanding of probiotics and their potential for preventing and treating health conditions is at an
early stage, but moving ahead. In November 2005, a conference that was cofunded by the National Center for
Complementary and Alternative Medicine (NCCAM) and convened by the American Society for Microbiology explored this
According to the conference report, some uses of probiotics for which there is some encouraging evidence from the
study of specific probiotic formulations are as follows:
- To treat diarrhea (this is the strongest area of evidence, especially for diarrhea from rotavirus)
- To prevent and treat infections of the urinary tract or female genital tract
- To treat irritable bowel syndrome
- To reduce recurrence of bladder cancer
- To shorten how long an intestinal infection lasts that is caused by a bacterium called Clostridium
- To prevent and treat pouchitis (a condition that can follow surgery to remove the colon)
- To prevent and manage atopic dermatitis (eczema) in children
The conference panel also noted that in studies of probiotics as cures, any beneficial effect was usually low; a
strong placebo effect often occurs; and more research (especially in the form of large, carefully designed clinical
trials) is needed in order to draw firmer conclusions.
Some other areas of interest to researchers on probiotics are
- What is going on at the molecular level with the bacteria themselves and how they may interact with the
body (such as the gut and its bacteria) to prevent and treat diseases. Advances in technology and medicine are
making it possible to study these areas much better than in the past.
- Issues of quality. For example, what happens when probiotic bacteria are treated or are added to foods—is
their ability to survive, grow, and have a therapeutic effect altered?
- The best ways to administer probiotics for therapeutic purposes, as well as the best doses and
- Probiotics' potential to help with the problem of antibiotic-resistant bacteria in the gut.
- Whether they can prevent unfriendly bacteria from getting through the skin or mucous membranes and
traveling through the body (e.g., which can happen with burns, shock, trauma, or suppressed immunity).
Side Effects and Risks
Some live microorganisms have a long history of use as probiotics without causing illness in people. Probiotics'
safety has not been thoroughly studied scientifically, however. More information is especially needed on how safe
they are for young children, elderly people, and people with compromised immune systems.
Probiotics' side effects, if they occur, tend to be mild and digestive (such as gas or bloating). More serious
effects have been seen in some people. Probiotics might theoretically cause infections that need to be treated with
antibiotics, especially in people with underlying health conditions. They could also cause unhealthy metabolic
activities, too much stimulation of the immune system, or gene transfer (insertion of genetic material into a
Probiotic products taken by mouth as a dietary supplementA product that contains vitamins, minerals, herbs or other
botanicals, amino acids, enzymes, and/or other ingredients intended to supplement the diet. The U.S. Food and Drug
Administration has special labeling requirements for dietary supplements. are manufactured and regulated as foods,
Saccharomyces boulardi (large cells) found along with bacteria in fermented fruit juice.
Photo Credit: SciMAT / Photo Researchers, Inc
Some Other Points To Consider
- If you are thinking about using a probiotic product as CAM, consult your health care provider first. No CAM
therapy should be used in place of conventional medical care or to delay seeking that care.
- Effects from one species or strain of probiotics do not necessarily hold true for others, or even for
different preparations of the same species or strain.
- If you use a probiotic product and experience an effect that concerns you, contact your health care
- You can locate research reports in peer-reviewed journals on probiotics' effectiveness and safety through
the resources PubMed and CAM on PubMed.
NCCAM-Sponsored Research on Probiotics
Among recent NCCAM-sponsored research are the following projects:
- Investigators at Tulane University School of Public Health and Tropical Medicine are studying the
effectiveness of selected probiotic agents to treat diarrhea in undernourished children in a developing
- At the Mayo Clinic College of Medicine, researchers have been examining probiotics for possibly decreasing
the levels of certain substances in the urine that can cause problems such as kidney stones.
- A team at Tufts-New England Medical Center is studying probiotics for treating an antibiotic-resistant type
of bacteria that causes severe infections in people who are hospitalized, live in nursing homes, or have
weakened immune systems.
Sources are primarily recent reviews on the general topic of probiotics in the peer-reviewed medical and scientific
literature in English in the PubMed database, selected evidence-based databases, and Federal Government
- 1994–2004 U.S. specialty/other supplement
sales. Nutrition Business Journal. 2005. Accessed on December 7, 2006.
- Alvarez-Olmos MI, Oberhelman
Probiotic agents and infectious diseases: a modern perspective on
a traditional therapy.
Clinical Infectious Diseases. 2001;32(11):1567–1576.
. Natural Medicines
Comprehensive Database Web site. Accessed on
December 7, 2006.
- Bifidus. Thomson MICROMEDEX AltMedDex
System. Web site Accessed on December 7, 2006.
- Cabana MD, Shane AL, Chao C, et
Probiotics in primary care
pediatrics. Clinical Pediatrics.
- Doron S, Gorbach SL.
Probiotics: their role in the treatment and prevention of
disease. Expert Review of Anti-Infective Therapy.
- Ezendam J, van Loveren H.
Probiotics: immunomodulation and evaluation of safety and
efficacy. Nutrition Reviews.
- Food and Agriculture Organization (FAO) of
the United Nations and World Health Organization (WHO). Guidelines for the Evaluation of Probiotics in Food. Report of a Joint FAO/WHO Working Group on Drafting Guidelines for the Evaluation of
Probiotics in Food. Accessed on December 7, 2006.
- Gill HS, Guarner F.
Probiotics and human health: a clinical
perspective. Postgraduate Medical Journal.
- Hammerman C, Bin-Nun A, Kaplan
Safety of probiotics: comparison of two popular
strains. BMJ. 2006;333(7576):1006–1008.
- Huebner ES, Surawicz CM.
Probiotics in the prevention and treatment of gastrointestinal
infections. Gastroenterology Clinics of North
- Lactobacillus . Natural Medicines Comprehensive
Database Web site. Accessed on December 7, 2006.
- Lactobacillus . Thomson MICROMEDEX AltMedDex
System Web site. Accessed on December 7, 2006.
- Probiotics: Bottom Line Monograph. Natural
Standard Database Web site. Accessed on December 7,
- Reid G, Hammond JA.
Probiotics: some evidence of their
effectiveness. Canadian Family Physician.
- Salminen SJ, Gueimonde M, Isolauri
Probiotics that modify disease
risk. Journal of Nutrition.
- Vanderhoof JA, Young RJ.
Current and potential uses of
probiotics. Annals of Allergy, Asthma, & Immunology.
2004; 93(5 suppl 3):S33–S37.
- Walker R, Buckley M.
Probiotic Microbes: The Scientific Basis. Report of an American Society for Microbiology colloquium; November 5–7, 2005; Baltimore, Maryland. American Society for Microbiology Web
site. Accessed on December 7, 2006.