Are Probiotics Good for You?


Please login to view this content , or sign up for an account

A recently published report by the American Gastroenterological Association (AGA) on Clinical Practice Guidelines for the role of probiotics in the management of gastrointestinal disorders, based on an in depth Technical Review of the published literature concludes that probiotics have little if any evidence based value in treating digestive diseases (including irritable bowel syndrome [IBS] and inflammatory bowel diseases),1 a statement that is not surprising to somebody who has long followed the scientific debate about probiotics and who gets the question from nearly all of my patients which probiotic is best to take. The only disease populations that the report exempts from their negative assessment were children and adults on antibiotic treatment, preterm infants with low birthweight and patients with pouchitis, a postoperative complication in patients following a colectomy.

According to the World Health Organization, “Probiotics are live microorganisms which when administered in an adequate dose confer a health benefit on the host.” This is an ambiguous definition, as it includes both the possible benefits of ingested microbes on gut and overall health in individuals without any specific gastrointestinal (GI) disorder (probably the majority of people who take probiotics), as well as the possible benefits in treating or preventing a specific disease (a small fraction of the overall market). Even though there are a number of clinical trials which have aimed to demonstrate an effect on GI disorders (most of which according to the report have not been conclusive, were of low quality or have been negative), there is a small number of studies which have shown that certain probiotics are effective in reducing common digestive symptoms such as rumbling and abdominal discomfort in otherwise healthy people.2 Unfortunately, for most probiotics such well designed and controlled studies do not exist.

Even though I generally agree with the conclusions of the AGA guidelines, there are several important points to consider before we close the curtain on the benefits of probiotics:

  • The same microbes may not be effective in everybody, and based on current knowledge, the effectiveness of a particular microbe is likely to depend on the unique composition and function of the gut microbiome of a particular individual. Until we are able to design custom cocktails of probiotic strains which match an individual’s microbiome, and evaluate the effectiveness in such selected populations it may be impossible to demonstrate significant benefits in clinical trials.
  • While in most people, orally ingested beneficial microbes are not able to colonize, e.g. make a permanent home in the gut of an individual, and are gone within 48 hours, they do persist in others.3 Again, we currently don’t know how to identify such individuals before deciding on a treatment.
  • People have strong belief systems about probiotics, similar to such beliefs in multivitamins and supplements. Strong beliefs are often associated with powerful placebo effects which make it difficult in a clinical trial to identify a specific probiotic effect.
  • Regular intake of fermented food, be it dairy, vegetables or fish dates back, and foods from fermented milk products date back about 8000–10,000 years and are popular in wide parts of the world. It is likely that the combination of valuable nutrients contained in these foods (including dietary fiber, polyphenols, and, in addition to the fermenting microbes enhance the benefit of such fermented foods.

As we currently don’t have an easy and reliable test to determine who will benefit from ingesting a particular microbial strain, I personally feel that the regular intake of naturally fermented foods, be it yoghurt, kefir, cheeses, kimchi or kombucha should be part of any healthy diet. These foods are not only tasty, but provide healthy benefits over and above possible microbe-mediated effects


  1. Grace L. Su et al. AGA AGA Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology.
  2. Denis Guyonnet et al. Fermented Milk Containing Bifidobacterium Lactis DN-173 010 Improved Self-Reported Digestive Comfort Amongst a General Population of Adults. A Randomized, Open-Label, Controlled, Pilot Study
  3. Niv Smora et al. Personalized Gut Mucosal Colonization Resistance to Empiric Probiotics Is Associated With Unique Host and Microbiome Features. Cell 2018; 174:1388-1405

Emeran Mayer, MD is a Distinguished Research Professor in the Departments of Medicine, Physiology and Psychiatry at the David Geffen School of Medicine at UCLA, the Executive Director of the G. Oppenheimer Center for Neurobiology of Stress and Resilience and the Founding Director of the Goodman-Luskin Microbiome Center at UCLA.