Probiotics and Prebiotics

As the potential health benefits of probiotics and prebiotics have come to light in recent years, many people are interested in learning what they are, how they work and the strength of the science behind the claims.
Probiotics and Prebiotics
Probiotics are beneficial bacteria which, when consumed in adequate amounts, provide a health benefit as the result of their presence in the gastrointestinal (GI) tract. The most common types of probiotics are strains of Lactobacilli and Bifidobacteria, which are found in yogurts and other cultured dairy products. Probiotics are also added to a variety of fortified foods and beverages and are available as dietary supplements.

Consumption of probiotics is thought to increase the number of helpful bacteria in the GI tract, while at the same time inhibiting the growth of harmful bacteria. This function has been linked to a broad range of potential health benefits. The most widely researched health benefit is in the area of anti-diarrheal effects, with the strongest evidence related to the use of particular probiotics strains in preventing and treating diarrhea illnesses in children.1 There is also some evidence to suggest that probiotics reduce symptoms of irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD)2 and help to alleviate the symptoms of lactose intolerance.3 This research has major limitations, however, because there are so many strains of bacteria and dosages used in the research that can vary widely, the benefits of one strain cannot necessarily be inferred from another. Additionally, too few human trials have been done to draw any firm conclusions.

Prebiotics are nondigestible food components that stimulate the growth and/or activity of beneficial bacteria ("probiotics") in the colon.4 In other words, prebiotics are the "food" for probiotics.

Prebiotics are found naturally in many foods (e.g. whole grains, onions, bananas, garlic, honey, leeks, and artichokes) and can also be extracted from plants (e.g. inulin from chicory root). Many prebiotics are added to processed foods and beverages and are available as dietary supplements.

Although their major function is to promote the growth of beneficial bacteria, certain prebiotics have been shown to increase the absorption of calcium.5 Furthermore, animal studies suggest that prebiotics may also have a favorable effect on the immune system.

Bottom Line
While research supports the beneficial effects of specific pre- and probiotics, conclusions are difficult to draw because benefits vary depending on the type and amount of prebiotic and probiotic consumed, and too few human trials have been done. Future studies using more consistent methods will provide a clearer understanding of their effects on health.


1 Salari P, Nikfar S, Abdollahi M. A meta-analysis and systematic review on the effect of probiotics in acute diarrhea. Inflamm Allergy Drug Targets. 2012 Feb;11(1):3-14.

2 Moayyedi P, Ford AC, Talley NJ, et al. The efficacy of probiotics in the treatment of irritable bowel syndrome: a systematic review. Gut 2010;59:325–32.

3 EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific opinion on the substantiation of health claims related to live yoghurt cultures and improved lactose digestion (ID 1143, 2976) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA J 2010;8:1763.

4 World Gastroenterology Organisation Global Guidelines. Probiotics and prebiotics. October 2011.

5 Scholz-Ahrens KE, Ade P, Marten B, et al. Prebiotics, probiotics, and synbiotics affect mineral absorption, bone mineral content, and bone structure. J Nutr. 2007 Mar;137(3 Suppl 2):838S-46S.