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Probiotics are a multibillion-dollar for-profit industry. But most people who take them are wasting their money.
I've seen wide-reaching promises about probiotics touted everywhere — in supermarkets, pharmacies, online and on television by "gut health experts," including fellow physicians. Proponents claim probiotics can boost your microbiome — the organisms that live inside your gut — and help with digestive issues, immune function and even mental health.
But the marketing claims about over-the-counter probiotics largely do not match the evidence. As a gastroenterologist, I rarely advise my patients to start a probiotic — much to their surprise. They're even more surprised when I tell them that's part of the evidence-based guidelines: The American Gastroenterological Association does not recommend probiotics for most digestive conditions.
Instead, here's what I do recommend: Eat a fiber-rich diet. This time-tested recommendation remains one of the strongest-studied ways to promote and preserve a healthy microbiome and improve your overall health.
Eating a low-fiber diet leads to the loss of major categories of bacteria — and once certain groups are lost, they can be lost for good, even if you try later to ramp up fiber intake later. So the time to act is now. The more diverse your diet, the more diverse your microbiome, and the healthier you are. So choose a variety of high-fiber plants, nuts and fermented foods to feed your microbiome the nutrient buffet it deserves.
Research on probiotics is all over the map
Officially, the term "probiotic" is defined as live microorganisms known to confer a health benefit. But of the more than 1,000 clinical trials of probiotics, there is vast heterogeneity across experiments — different bacterial strains, different doses and different outcomes being measured. Some take characteristics of the host microbiome into account; others don't, focusing more on symptoms or other health measures.
This creates a confusing research landscape peppered with both positive and negative results. Even when aggregated into meta-analyses, the results are all over the map.
The Food and Drug Administration doesn't consider over-the-counter probiotics to be drugs, so unlike medications, they don't have to go through the process of rigorous testing and clinical trials. This issue also comes up when scientists seek to draw conclusions about skin care products or other supplements, which also aren't regulated as drugs by the FDA.
The promise of the microbiome
Microbiome science as we know it took off in the early 2000s when researchers recognized how many healthy bacteria — not the kinds that cause a sudden major infection — reside inside our guts. Shortly afterward, the National Institutes of Health laid the groundwork for the Human Microbiome Project, a major initiative to sequence and improve our understanding of the microbiome, from which many discoveries were made about diseases influenced by our gut bacteria.
In theory, it would logically follow, altering the bacterial composition of the microbiome, possibly through the introduction of live microorganisms, could benefit our health. But achieving that has been easier said than done.
Probiotics — or other ways to modulate the microbiome, such as fecal transplant — have incredible potential, but realizing that potential is still a nascent scientific field in many ways. Each of our microbiomes, medical history and diets is unique. We still need rigorous studies that would allow us to personalize such treatments for individuals.
Why misinformation is rampant
When it comes to probiotics, commercial interests have outpaced the science. This uncomfortable disconnect has been known to gastroenterologists and microbiome scientists for many years. One common tactic by marketers is to blur data from one probiotic into the purported benefits of the one being sold — as if all probiotic types fall neatly under one big umbrella.
Misinformation about probiotics is common on social media. A 2023 study that looked at 100 YouTube videos about probiotics found that 95 percent of the videos endorsed a positive attitude toward their consumption — with far more content produced by amateurs than by experts. And a 2021 study found that discussions of probiotics on X (formerly Twitter) were dominated by advertisements and promotions rather than by scientists or policymakers.
Who should take probiotics?
There are a few very specific scenarios where clinical guidelines support the use of probiotics in adults. Those are:
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It should be noted that the guidelines do not recommend even these indications very strongly — and that the quality of evidence upon which they're based was rated "low" or "very low."
What I want my patients to know
Some patients tell me they do feel better after taking probiotics. Your own experience is valid — a fraction of people do experience a benefit. In these cases, I tell my patients I'm glad they've found something that has helped them and feel reassured if they've bought a probiotic from a company vetted by a third-party.
But more often, I see patients experiencing some symptom — perhaps bloating or belly pain — and they started taking a probiotic to see if it would help. Several hundreds of dollars later, the symptoms persist. That's a good moment for us to pause and consider the data together.
Trisha S. Pasricha is a physician at Massachusetts General Hospital, an instructor in medicine at Harvard Medical School and a medical journalist.
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