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Probiotics and IBS: What does the research say?

By Published 4 min read

Irritable bowel syndrome, also called IBS, causes stomach pain and changes in bowel habits, often together with wind and bloating. Many people with IBS try probiotics, and it is easy to see why: gut bacteria are often mentioned as a possible explanation.

But does it help? The answer depends on who you ask. Here is what the trials show, and why the experts do not agree.

Many trials, but few firm answers

A large review from 2023 pooled 82 trials with 10,332 adults with IBS. Only 24 of the trials had a low risk of bias on every point [1].

The result was mixed:

  • For bacteria of the genus Escherichia, there was moderate certainty that they relieved overall symptoms.
  • For Lactobacillus strains, among them L. plantarum 299v, the certainty was low.
  • For combination products with several strains, the certainty was very low. This also applied to bloating.
  • Side effects were no more common with probiotics than with placebo (55 trials, over 7,000 patients).

The authors' own conclusion: some combinations or strains may help, but the certainty of the evidence was low to very low in almost all the analyses [1].

A basic problem is that almost every trial tests something different. The American Gastroenterological Association reviewed 55 trials and found 44 different strains or combinations. For most probiotics, then, all the evidence rests on one single trial [2].

Four societies, four different recommendations

When medical societies write guidelines, they read the same trials. Even so, they have reached very different recommendations:

Society Advice on probiotics for IBS
British (BSG 2021) Probiotics as a group may help with overall symptoms and stomach pain, but no particular strain can be recommended. It is reasonable to try them for up to 12 weeks and stop if they do not help. Weak recommendation, very low quality [3].
Canadian (CAG 2019) Suggests offering probiotics. There is not enough evidence for any particular species, so try them for a limited period, e.g. a month. Conditional recommendation, low quality [4].
American (ACG 2021) Suggests not using probiotics for overall IBS symptoms. Conditional recommendation, very low quality [5].
American (AGA 2020) Recommends probiotics for IBS only as part of a clinical trial. No recommendation, because of a knowledge gap [6].

Why do they disagree? Because the evidence is weak, and because it points in several directions. If you pool all the trials, probiotics seem to help a little. If you look at a single strain, there is rarely more than one or two trials. Whether you then say "try it" or "don't" probably depends on how much weight you give to cost, safety and the patient's own wishes.

Note that none of the four recommends a particular strain or a particular product.

What has better evidence

The same guidelines point to other treatments with better evidence than probiotics:

  • Soluble fibre, e.g. psyllium (psyllium husk), has a strong recommendation in the British guideline, based on moderate-quality evidence. Start with a low dose of 3 to 4 grams a day and increase slowly to avoid bloating. Insoluble fibre such as wheat bran, on the other hand, should be avoided, because it can make symptoms worse [3].
  • A low-FODMAP diet can help as a next step, but it should be planned by a dietitian, and foods should be reintroduced according to what you tolerate [3].

Read more in the articles on prebiotics and types of fibre and on bloating.

If you want to try probiotics

According to the British and Canadian guidelines, it is reasonable to try them if you want to [3][4]. Do it in a way that lets you actually see whether it works:

  1. Choose a strain that has been tested in IBS trials, rather than a product with many strains and big numbers on the label. Read about what the numbers mean in the article on CFU and bacterial strains.
  2. Set a time limit. The British guideline says up to 12 weeks, the Canadian one e.g. a month [3][4].
  3. Keep track of your symptoms before and during, so you are not just going by a feeling.
  4. Stop if it does not help. There is no reason to keep paying for something that does not work for you.

If you are seriously ill or have a weakened immune system, first read the article on who should not take probiotics.

A diagnosis first

IBS must be diagnosed by a doctor. Among other things, the British guideline recommends blood tests and a test for coeliac disease when you first see your doctor with the symptoms [3]. Other diseases can cause the same symptoms.

If you have blood in your stools, unintended weight loss or other warning signs, see your doctor before you start experimenting. See the list of warning signs in the article on bloating.

The bottom line

  • Over 80 trials have tested probiotics for IBS, but the certainty of the evidence is low to very low for almost all products.
  • Most strains have been tested in only one trial.
  • The British and Canadian medical societies say it is reasonable to try them for a limited period. The two American ones say no, or only in trials.
  • None of them recommends a particular strain.
  • Soluble fibre such as psyllium has better evidence and a stronger place in the guidelines.

Sources

  1. Goodoory VC et al. Efficacy of Probiotics in Irritable Bowel Syndrome: Systematic Review and Meta-analysis. Gastroenterology. 2023. PMID 37541528
  2. Preidis GA et al. AGA Technical Review on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020. PMID 32531292
  3. Vasant DH et al. British Society of Gastroenterology guidelines on the management of irritable bowel syndrome. Gut. 2021. PMID 33903147
  4. Moayyedi P et al. Canadian Association of Gastroenterology Clinical Practice Guideline for the Management of Irritable Bowel Syndrome (IBS). J Can Assoc Gastroenterol. 2019. PMID 31294724
  5. Lacy BE et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol. 2021. PMID 33315591
  6. Su GL et al. AGA Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020. PMID 32531291

This article is general information and not medical advice.