Probiotics and health: a review of the evidence


Probiotics comprise a large number of different strains of bacteria and other microorganisms, such as yeasts. When taken in adequate amounts, these live microorganisms confer a health benefit. Probiotics have been consumed for thousands of years, and are now widely available for consumers in various forms, including capsules and dairy products.


The health effects of probiotics have been applauded as ‘miraculous’ one minute and labelled with ‘misleading health claims’ in another. It is no wonder that there is widespread confusion amongst consumers. To help address this confusion, the British Nutrition Foundation (BNF) has published a scientific review - Probiotics and health: a review of the evidence - to draw together complex probiotic research. Dr Elisabeth Weichselbaum, author of the review, examined around 100 original research studies and reviews on probiotics and health. The effects of probiotics on a wide range of health conditions were considered: inflammatory bowel disease; irritable bowel syndrome; constipation, acute and antibiotic-associated diarrhoea; the common cold; and allergy. The scientific review has been peer reviewed and now appears in the December issue of the Nutrition Bulletin.

Probiotics is a complex area, and when considering the results of research in this field it is important to consider a number of factors:


  • Probiotics encompass a wide range of bacterial strains

Speaking about probiotics in general can be misleading because health effects may be specific to a single strain of bacteria. It is important to remember that each single strain has to be tested for each single health outcome. Of course, scientific research has investigated the effects of many different probiotic strains on different health outcomes. The BNF review helps to unravel this complexity and indicates which strains have been shown to be effective for different health outcomes.


  • Probiotics must be taken regularly and survive their passage through the gastro-intestinal tract

To be effective and have an impact on health, probiotics must also be able to survive the harsh conditions during their passage through the intestinal tract. Once they reach the gut, and become established they can then influence the balance of the gut microflora. To become established in the gut, probiotic strains need to be taken frequently, as they generally persist in the gut for only a short time.


  • The vehicle by which probiotics are delivered, and dose, are also important

It is also important to investigate whether probiotics are able to deliver health benefits in the vehicle through which they are delivered (e.g. capsules, dairy products etc). It is also important to consider the dose required to allow the probiotic to establish in the gut microflora, and so exert a health effect.



Overall, the results of the review show accumulating evidence to support the health benefits of probiotics in some areas. The results have been summarised in a series of BNF factsheets (see attachments), to help support health professionals. These valuable resources can be used to underpin consistent health advice on probiotics.


See the full review for further details:

Weichelbaum E (2009) Probiotics and health: a review of the evidence. Nutrition Bulletin 34: 340-373.

Last reviewed November 2009. Next review due June 2013.