More Evidence That Yogurt Isn’t the Gut Magician You Think It Is

A new study examines the probiotic dosages of more than 100 foods.
April 25, 2017, 4:54pm
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Probiotics are a real nutrition darling these days. These "good bacteria" can allegedly improve a whole host of bodily functions, including digestion and immunity. The science is complicated and still in its early stages, but it's not all hype: A number of clinical trials show that there are real, measurable effects of altering the makeup of a person's gut bacteria. That's led many people to seek out probiotics; according to one report, the global market climbed past $35 billion in 2015.


But there's a disconnect between those clinical trials and many of the probiotic options you'll find in stores: The dosages in probiotic foods are so low, it's hard to know whether they're providing any health benefit at all.

In the most recent study looking at this issue, researchers set out to do two things: Document the dosage and prevalence of probiotic strains in the Canadian food supply, and then, based on a survey of the scientific literature, understand what health benefits consumers could potentially expect from probiotics in their food.

For the first part of the new study, researchers looked at a database of food package label information across the country's three largest grocery stores, accounting for more than 75 percent of the Canadian food supply. They examined nearly 100 probiotic-containing products, cataloging information about species, strains, and dosage.

Then they combed through the available clinical trials to understand the state of the science around probiotics. They found, for example, that food company Danone had funded 11 studies about its proprietary strain that showed healthy side-effects such as decreased incidence and duration of infectious diseases. The dosages used in those studies, however, were up to three times that found in the dairy drink containing the same strain.

Anecdotally, the current thinking is that a given probiotic product should contain at least 1 billion CFUs—or colony forming units, a way of measuring viable bacterial cells—to make any appreciable changes in a person's health. And indeed, many of the products researchers have tested, such as probiotic yogurt, meet that benchmark of between 1 and 10 billion CFUs.

But since the dosages used in studies are often so much higher—in many cases, around 20 billion CFUs—it's hard to know if the benefits actually translate when people ingest just one or two billion. Scientists are also working through which particular strains of bacteria are the most useful, and how much of them are needed, to help treat any given ailment.

In the new study, this led the researchers to conclude that "many dosages are too low to provide the benefits demonstrated in clinical trials. Further research is needed to enable more effective use of these functional foods." That's one way of saying that probiotics show a lot of potential in the lab, but we're still working out the complex question of how they might help us in everyday life.

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