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Go with Your Gut: Understanding Probiotics1

Wendy J. Dahl and Volker Mai2

What are probiotics?

Probiotics are known as "good bacteria." Often, when we think of bacteria, we think about the ones that cause illness, and while there are many bacteria that can cause disease, there are many more that are beneficial to our health. Probiotics are live microorganisms that, when administered in adequate amounts, provide a health benefit.(1)

Many probiotics are Lactobacillus or Bifidobacterium species. Some common probiotic bacteria are listed below:

  • Lactobacillus acidophilus

  • Lactobacillus casei

  • Lactobacillus rhamnosus

  • Bifidobacterium longum

  • Bifidobacterium infantis

  • Bifidobacterium breve

  • Bifidobacterium bifidum

Some yeasts can also be probiotics. A common probiotic yeast is Saccharomyces boulardii.

What are the benefits of probiotics?

Figure 1. 

Probiotics help keep the balance of bacteria in our gastrointestinal tracts in check.


Volker Mai

[Click thumbnail to enlarge.]

The balance of bacteria in our gastrointestinal tract may be disturbed by a change in diet, contaminated food, stress, antibiotics, or aging. Probiotics can help restore and maintain intestinal balance. Probiotics may help prevent diarrhea that is associated with taking antibiotics. (2) Probiotics may also help prevent constipation (3) and help manage symptoms of gastrointestinal diseases such as ulcerative colitis. (4)

Figure 2. 

Lactobacillus rhamnosus R0049


Courtesy of Dr. Alexandra Smith Department of Food Sciences, University of Guelph. Copyright is held by Institut Rosell inc., Montreal, QC. Reproduced with permission.

[Click thumbnail to enlarge.]

How do probiotics work?

Probiotics promote health by:

  • Producing substances in the gut, such as lactic acid, that help to slow the growth of disease-causing bacteria.

  • Competing with disease-causing bacteria for nutrients and space.

  • Breaking down toxins.

  • Affecting the nerve and muscle function of the gut.

But probiotics do not live permanently in the gut—they need to be ingested frequently if they are to exert their beneficial effects.

What makes a good probiotic?

Probiotics need to be alive when they reach the gut. A good probiotic, therefore, needs to be able to survive the acidic environment of the stomach and resist other bacteria.

A good probiotic must also be safe. To ensure safety, probiotics must be accurately identified, free from contamination, and labeled properly. Probiotics are tested to make sure they do not cause stomach upset, diarrhea, or other side effects. Also, probiotics are tested further to make sure they have positive effects on human health.

Are there risks in taking probiotics?

Probiotics are considered to be safe for healthy people. However, people with compromised health or suppressed immune function, such as individuals with HIV/AIDS and those who have undergone a transplant or are currently being treated for cancer, should consult their doctors before taking a probiotic.(5)

Shopping for Probiotics

Probiotics are available in capsules and as powders. Probiotics are added to some foods such as some yogurt brands. Probiotics may also be found in specialty fermented milk beverages, snack bars, fruit drinks, and breakfast cereals.


Probiotics are live microbes with health benefits. They are effective in maintaining and restoring the balance of microbes in our gastrointestinal tract. With more research, other health benefits may be found.


(1) 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.

(2) Issa I, Moucari R. 2014 Probiotics for antibiotic-associated diarrhea: Do we have a verdict? World J Gastroenterol 20(47): 17788-17795

(3) Dimidi E, Christodoulides S, Fragkos KC, Scott SM, Whelan K. 2014 The effect of probiotics on functional constipation in adults: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr. 100(4):1075-84.

(4) Ghouri YA, Richards DM, Rahimi EF, Krill JT, Jelinek KA, DuPont AW. 2014 Systematic review of randomized controlled trials of probiotics, prebiotics, and synbiotics in inflammatory bowel disease. Clin Exp Gastroenterol. 7:473-87.

(5) Hempel S, Newberry S, Ruelaz A, Wang Z, Miles JN, Suttorp MJ, Johnsen B, Shanman R, Slusser W, Fu N, Smith A, Roth B, Polak J, Motala A, Perry T, Shekelle PG. 2014 Safety of probiotics used to reduce risk and prevent or treat disease. Evid Rep Technol Assess (Full Rep); (200): 1-645.



This document is FSHN11-11, one of a series of the Food Science and Human Nutrition Department, UF/IFAS Extension. Original publication date June 2011. Revised October 2015. Visit the EDIS website at


Wendy J. Dahl, PhD, assistant professor, Food Science and Human Nutrition Department; and Volker Mai, PhD, assistant professor, Emerging Pathogens Institute; UF/IFAS Extension, Gainesville, FL 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.