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The Shaky Science of Probiotic Supplements
You may be better off with kimchi and kombucha
The human body is home to trillions of microorganisms. They carpet the skin, coat the nose and mouth, and saturate the gastrointestinal tract. Researchers have long recognized that these microbes — particularly the ones in the gut — play a role in human health. But it wasn’t until June 2012 that the veil was truly lifted from the eyes of the general public and the medical science community.
That month, the National Institutes of Health announced preliminary findings from its $170 million Human Microbiome Project (HMP). The project’s stated goal was “to further our understanding of how the microbiome impacts human health and disease,” and it did that in part by mapping the genetic makeup of the microorganisms living in and on 242 healthy volunteers. Those maps revealed that the microbiome contributes more genes that are “responsible for human survival” than do the body’s own cells. The HMP also provided scientists with a healthy reference model against which to compare the microbiomes of sick individuals.
Right away, researchers started contrasting the microbiomes of the well and unwell. (This line of research wasn’t new, but it became both more reliable and more commonplace.) Many of these studies found that the gut microbes of sick people differed from those of healthy people in predictable ways. These discoveries helped popularize the idea that by improving the makeup of the microbiome, a person could sidestep or treat a wide range of medical conditions — everything from obesity and viral infections to depression.
Enter probiotic supplements. By definition, a probiotic is something that contains live microorganisms that confer a health benefit on their “host.” And the presumption among consumers and, at least initially, among many doctors was that ingesting certain bacteria could reshape or repopulate the gut’s ecosystem of bacteria in ways that improve a person’s health. Unfortunately, this presumption has turned out to be wrong.
“The old story that you can just pump a bunch of good bacteria in and they’ll replace the bad is not accurate,” says Dr. Emeran Mayer, a professor of medicine and co-director of the Digestive Diseases Research Center at UCLA. “People think that…
