With everything from yogurt to mattresses labeled “probiotic,” how can consumers know which products have proven health benefits?

Americans doing their grocery shopping confront an ever-growing number of products claiming to be “probiotic,” but they may be confused about what the label really means.

Their confusion is legitimate, according to a team of doctors and microbiologists who recently published a set of recommendations for the government agencies that regulate such health claims. The report suggests that products should meet stricter requirements before they can claim that they contain probiotics, or beneficial bacteria, such as those commonly found in yogurt.

Interest in probiotics has expanded well beyond yogurt to kombucha tea, kefir, kimchi, and even probiotic supplements as evidence has grown indicating that the balance of bacteria in our digestive tracts influences our health and metabolism in a number of ways.

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Probiotics, unlike many faddish health foods, are often recommended by doctors. Patients with diarrhea and bowel disorders, including irritable bowel syndrome, are most likely to be told to add probiotics to their diet. But even clinicians struggle to provide more specific information in the absence of rigorous scientific studies on which good bacteria are best and in what dosage.

Sending a patient to the grocery store to buy probiotics is akin to sending someone to Mexico in search of chiles.

“People say ‘Where do I even start?’ and it’s hard to make recommendations,” said Katie Ferraro, a registered dietitian and nursing professor at the University of California, San Francisco.

As the claims about their health benefits have grown and consumers have begun buying more probiotics, companies have capitalized by adding the term to other product labels—including those on some shampoos, disinfectants, and even mattresses.

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Consumers could benefit from stricter labeling requirements for probiotic products, according to dietitian Susan Weiner.

“Consumers should be informed about the contents of these products, including side effects, effectiveness, and dosage. In addition, research on the validity of products should be made available, not just manufacturers’ claims,” Weiner said.

The International Scientific Association for Probiotics and Prebiotics, a nonprofit supporting scientific research on the benefits of probiotics, convened experts from U.S., European, and Canadian companies and universities in response to these concerns to chart the what’s what of the friendly bacteria.

The U.S. Food and Drug Administration (FDA) doesn’t have any special requirements for foods that claim to be probiotic, a spokeswoman said. And the United Nations and the World Health Organization last offered guidance on probiotics in 2002.

“The science has really changed in the last 12 years,” said Daniel Merenstein, a professor of family medicine at Georgetown University and one of the authors of the new report. “With genetic, microbiome, and clinical studies, a lot has really progressed. We thought it was necessary to discuss this science, review the definition, explain core benefits, etc.”

They found that the most common probiotic strains do indeed help with overall digestion, including with ulcerative colitis, infectious and antibiotic-associated diarrhea, and irritable bowel syndrome.

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The bacteria with the most evidence to support their health claims include Lactobacillus acidophilus, casei, fermentum, gasseri, johnsonii, paracasei, plantarum, rhamnosus, and salivarius, as well as Bifidobacterium adolescentis, animalis, bifidum, breve, and longum.

But, for any food to be considered probiotic, it must contain active cultures of these bacteria in adequate numbers at the time the food is consumed, the authors cautioned. To have an effect, the cultures should number at least 1 billion colony forming units, or CFU, per serving.

For Ferraro, dosage was a great place to start.

“The biggest problem with probiotics is that nobody can agree with what an efficacious dose is,” she said.

But setting an upper limit could be just as important as setting a lower limit, according to Ferraro.

“Are there going to be upper limits sets like there are with vitamins and minerals? Because too much of a good thing is not a good thing,” she said.

The new recommendations could challenge the labeling of some types of yogurt. Yogurt could not claim to be probiotic unless it contained these specific types of bacteria in adequate numbers. Although yogurt has well-documented health benefits, the report notes, not enough evidence links those benefits to particular kinds of bacteria.

Products that don’t contain the specific strains widely recognized as having health benefits should therefore be labeled simply as “containing live and active cultures.”

Some products also make claims about probiotics that go beyond digestive health. Some advocates claim that probiotics help boost overall immune function, for example. But the expert review found this claim too broad to be included on product labels.

One bacterial strain may help with one immune-related function—inflammation, for example—and another with fighting off colds. The panel found that probiotic bacteria don’t have a general impact on the immune system, despite its benefits for digestive health.

“You can’t measure immunity; it would be overreaching beyond the area of the gut to claim that they’re helpful. It’s a very nebulous claim that you can’t prove or disprove, which is why manufacturers use it,” Ferraro said.

The report is an expert opinion, but no more than that, Merenstein explained. It won’t have any immediate effect on FDA requirements for how products are labeled, but it does provide scientific groundwork to inform any regulatory bodies that revisit the issue.

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