Supplements · 4 min read ·

Probiotics: they help, but only sometimes

Live bacteria in capsules promise a healthy gut and immunity. Studies show a few situations where they work — and many where nobody knows.

In a nutshell

1What probiotics are

By the FAO/WHO definition, probiotics are “live microorganisms which when administered in adequate amounts confer a health benefit on the host”.1 Most often they are bacteria of the genera Lactobacillus and Bifidobacterium.3

2Diarrhoea after antibiotics

Moderate evidence — Cochrane 19% → 8% A review of 33 trials with 6,352 children: with probiotics, 8% of children got antibiotic-associated diarrhoea, without them 19%. Higher doses, at least 5 billion bacteria a day, worked better. No serious adverse effects appeared in the trials.2
Moderate evidence −37% A summary of 42 trials with 11,305 adults: probiotics taken with antibiotics reduced the risk of diarrhoea by 37%. Higher doses and only some species helped, mainly lactobacilli and bifidobacteria; in people at low risk of diarrhoea there was no difference.3

3Gut and digestion

Moderate evidence — expert consensus 70 studies A review of 70 studies and an international panel consensus: specific probiotics can ease symptoms and abdominal pain in some people with irritable bowel syndrome. But many newer products did not help.4
Weak evidence 7 studies A review of 7 randomised trials in healthy adults: probiotics did not change the diversity or composition of gut bacteria compared with placebo.5

4Immunity and metabolism

Weak evidence — Cochrane 12 studies A review of 12 trials with 3,720 people: with probiotics, fewer people had an acute upper respiratory tract infection and the illness was shorter. The quality of evidence was low.6
Moderate evidence −0.9 kg A summary of 105 trials: in overweight (not obese) people, probiotics reduced weight by 0.9 kg on average, and in people with type 2 diabetes they slightly lowered blood sugar. The effects were small.7

What to take from this

Sources

Written on , based on studies available at that date. Newer research may change the conclusions.

  1. Hill C. et al. (2014). The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol 11:506–514. doi.org/10.1038/nrgastro.2014.66
  2. Guo Q. et al. (2019). Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database Syst Rev 4:CD004827. doi.org/10.1002/14651858.CD004827.pub5
  3. Goodman C. et al. (2021). Probiotics for the prevention of antibiotic-associated diarrhoea: a systematic review and meta-analysis. BMJ Open 11:e043054. doi.org/10.1136/bmjopen-2020-043054
  4. Hungin A. P. S. et al. (2018). Systematic review: probiotics in the management of lower gastrointestinal symptoms — an updated evidence-based international consensus. Aliment Pharmacol Ther 47:1054–1070. doi.org/10.1111/apt.14539
  5. Kristensen N. B. et al. (2016). Alterations in fecal microbiota composition by probiotic supplementation in healthy adults: a systematic review of randomized controlled trials. Genome Med 8:52. doi.org/10.1186/s13073-016-0300-5
  6. Hao Q., Dong B. R., Wu T. (2015). Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev CD006895. doi.org/10.1002/14651858.CD006895.pub3
  7. Koutnikova H. et al. (2019). Impact of bacterial probiotics on obesity, diabetes and non-alcoholic fatty liver disease related variables: a systematic review and meta-analysis of randomised controlled trials. BMJ Open 9:e017995. doi.org/10.1136/bmjopen-2017-017995

This is general information and does not replace a doctor. If your immunity is weakened, you are seriously ill or have a central venous catheter, take probiotics only after talking to a doctor.