Do You Need a Probiotic? What the Research Says (and When It Doesn’t Help)

Yogurt, kimchi, and kefir, fermented foods that contain live cultures

Probiotics are clearly useful in only a few specific situations, such as preventing a serious infection in people taking antibiotics. The major gastroenterology guidelines don’t support them for irritable bowel syndrome (IBS), Crohn’s disease, or ulcerative colitis. For everyday gut health, the evidence for supplements is weaker than the marketing suggests, while fermented foods have some promising research. Here’s what the guidelines actually say, who might benefit, and how to choose wisely.

What Are Probiotics?

Probiotics are live microorganisms, usually bacteria or yeasts, that may offer a health benefit when you take enough of them. The American Gastroenterological Association (AGA) estimated that 3.9 million American adults used some form of probiotics or prebiotics in 2015, four times as many as in 2007.

The key point is that “probiotics” isn’t one thing. Different strains do different things, which is why the AGA’s guideline evaluated each strain or combination separately instead of lumping them together.

When Probiotics May Help

The AGA’s 2020 guideline, the first to review probiotics across multiple digestive conditions, found enough evidence to make conditional recommendations in three situations:

SituationWhat the AGA suggestsEvidence quality (as rated)
Adults and children taking antibioticsSpecific probiotics (Saccharomyces boulardii or certain multi-strain combinations) to help prevent C. difficile infectionLow
Pouchitis (a complication after surgery for ulcerative colitis)A specific 8-strain combinationVery low
Preterm, low-birthweight infantsA specific combination to reduce necrotizing enterocolitis and deathModerate to high

A few things to know:

  • Strain matters. The recommendations apply to named strains, not to any probiotic on the shelf.
  • Antibiotics: The guideline notes that people who are immunocompromised, or at low risk for C. difficile infection, may choose not to use any probiotics. Talk to your doctor.
  • Preterm infants: This is hospital care managed by a neonatal team, not something to buy for a baby.

When the Evidence Doesn’t Support Them

  • IBS: The American College of Gastroenterology’s 2021 guideline recommends against probiotics for overall IBS symptoms, a conditional recommendation based on very low-quality evidence. The AGA says to use them only in clinical trials. The same ACG guideline did recommend peppermint oil for IBS, although also with low-quality evidence.
  • Crohn’s disease and ulcerative colitis: The AGA recommends probiotics only in clinical trials and suggests that people taking them for these conditions consider stopping, because of the cost and because there isn’t enough evidence to rule out harm.
  • Treating a C. difficile infection: Only in clinical trials.
  • Children with acute infectious gastroenteritis (a stomach bug): The AGA doesn’t suggest probiotics, noting that this differs from some other medical societies.

What About Healthy People?

The AGA guideline focused on digestive conditions, not general wellness. Even so, the panel chair said it underscores that the public’s assumptions about the benefits of probiotics aren’t well-founded.

A study from the Weizmann Institute of Science adds a note of caution. After a course of antibiotics, the microbiomes of people who did nothing returned to normal in about three weeks, while those who took a probiotic supplement had less diverse gut microbes. A Stanford researcher commented that probiotics can help some people and make things worse for others. One study isn’t the final word, but it’s a reminder that more bacteria isn’t automatically better.

Fermented Foods: A Promising Alternative

A randomized trial from Stanford, published in Cell in 2021, assigned 36 healthy adults to a 10-week diet rich in either fermented foods or fiber. The fermented-food group’s gut microbial diversity increased, with stronger effects at larger servings, and levels of 19 inflammatory proteins fell. Four types of immune cells also showed less activation. The foods included yogurt, kefir, fermented cottage cheese, kimchi, other fermented vegetables, and kombucha.

The high-fiber group saw less pronounced changes in microbiome diversity, and the authors said that raising fiber intake alone over a short time wasn’t enough to increase diversity. That doesn’t make fiber less valuable. The study lasted only 10 weeks, and fiber has well-documented long-term benefits. See our guide to how much fiber you need a day.

Some caveats: the study was small, short, and in healthy adults, and it showed changes in markers, not proof that fermented foods prevent disease. The researchers described it as a proof of concept.

If you want to try fermented foods, start with yogurt, kefir, kimchi, or sauerkraut. Greek yogurt and cottage cheese also count toward your daily protein, so see how much protein you need a day. Check labels, since some shelf-stable versions are heat-treated and no longer contain live cultures.

If You Decide to Take a Probiotic

  • Ask your doctor first, especially if you have a weakened immune system or a serious illness. The AGA noted that probiotics may not be suitable for people at high risk of infection.
  • Match the strain to the purpose. Look for strain-level names on the label, not just “probiotic blend.”
  • Know that quality varies. Harvard Health has pointed out that it’s unclear whether over-the-counter probiotics are high quality, and some lower-quality products may not contain the bacteria listed on the label.
  • Remember what we know about safety. Most safety research is on Lactobacillus and Bifidobacterium, and less is known about other strains.
  • Don’t take them indefinitely out of habit. If you don’t notice a benefit, it’s reasonable to stop.

When to See a Doctor

Tell your doctor about any probiotic you take. See a doctor if digestive symptoms last for weeks, come with pain or unexplained weight loss, or change your bowel habits. If bloating is your main complaint, start with the everyday habits that cause bloating.

The Bottom Line

Probiotics can be worth considering in a few specific situations, like preventing C. difficile infection while on antibiotics, but guidelines don’t support them for IBS, Crohn’s, or ulcerative colitis. For everyday gut health, a diet with fermented foods and plenty of fiber has better support than a generic supplement. If you do take one, choose a specific strain for a specific reason, and ask your doctor.

Frequently Asked Questions

Do probiotics actually work?
It depends on the strain and the condition. The AGA supports specific probiotics in a few situations, but not for IBS, Crohn’s disease, or ulcerative colitis.

Should I take a probiotic with antibiotics?
The AGA suggests specific probiotics to help prevent C. difficile infection in adults and children on antibiotics. People at low risk or with weakened immune systems may choose not to. Ask your doctor.

Do probiotics help IBS?
The ACG’s 2021 guideline recommends against them for overall IBS symptoms, and the AGA recommends them only in clinical trials.

Are fermented foods better than probiotic supplements?
A Stanford trial linked fermented foods to more diverse gut microbes and fewer inflammatory markers, but it was small and short. Neither has been proven better for general health.

Who should avoid probiotics?
People at high risk of infection, such as those with weakened immune systems or serious illness, should ask a doctor first.

Do probiotics help with bloating?
There’s no general recommendation, and results vary by strain. Start with the everyday habits that commonly cause bloating.

AUTHORITATIVE SOURCES

  • Gastroenterology (2020): Su GL, et al., “AGA Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders”
  • Gastroenterology (2020): Preidis GA, et al., AGA Technical Review on the role of probiotics
  • American Gastroenterological Association: “AGA does not recommend the use of probiotics for most digestive conditions” (news release)
  • NCCIH (NIH): “Irritable Bowel Syndrome and Complementary Health Approaches: What the Science Says” (citing the ACG 2021 guideline)
  • American College of Gastroenterology: Clinical Guideline on the Management of Irritable Bowel Syndrome (2021)
  • Cell (2021): “Gut-microbiota-targeted diets modulate human immune status” (Stanford University School of Medicine)
  • Weizmann Institute of Science study on probiotics after antibiotics, as reported by The Washington Post and Harvard Health Publishing

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