"It depends how you define a probiotic," says Gregor Reid, a professor of microbiology and immunology at the University of Western Ontario in Canada, and director of the Canadian Research and Development Center for Probiotics. "I would argue that probiotics are beneficial organisms that humans have evolved with and that are naturally present in the healthy gut."
These include Lactobacillus and Bifidus bacteria, which produce short-chain fatty acids that research suggests may be beneficial to health, help modulate immunity, and keep pathogenic organisms in check. A healthy diet rich in prebiotic fibers — plant fibers that we don't digest, but the good bacteria in our gut do metabolize and thrive on — and fermented foods such as kefirs, yogurts, and sauerkraut helps maintain healthy digestive function, says Reid.
But some claims outpace the science, he says, especially for novel organisms such as Bacillus coagulans, a soil-based organism that is stable when heated or pasteurized. Most probiotics are inherently fragile and must be protected from excess heat. The stability of B. coagulans, along with the fact that the organism is technically vegan (not isolated from a mammal's gut), has made it a popular addition in many designer probiotic products — including the aforementioned breakfast burrito (from Get Cultured) and pressed probiotic water (from Suja Juice).
B. coagulans is even included in a butter substitute called Melt, which advertises that it "delivers active cultures more effectively than yogurt." Organism per organism, this may be true, simply because of heat resistance. But Reid says, "We don't know what role this organism plays in healthy people. Why do you want to take it in the first place? Until scientists definitively show in human studies what it really does for you, I wouldn't recommend it for anybody."
Others beg to differ.
"Probiotics do not necessarily have to be native to our guts," says food microbiologist Glenn Gibson of the University of Reading in London. Microbiota in humans vary across individuals and cultures, so what is a native and natural inhabitant of one person's gut may not even live in another person's gut.
What matters, he says, is that they "are safe and beneficial." And B. coagulans, he asserts, passes that test.
"There is good research showing it improves gut health in the elderly and inhibits pathogens. We've done a few of those studies ourselves," Gibson says.
And while it's true that the organisms in your food need to survive in the finished product for you to get a benefit from consuming them, the absolute number of microbes in your meal may not be as important as we're led to believe, Gibson says. "We already know that bacterial pathogens can exert effects at tiny doses, so why wouldn't we expect the same of probiotics?"
Gastroenterologist Eammon Quigley of Houston Methodist Hospital in Houston, who specializes in the impact of probiotics on functional bowel disease and metabolic liver disease, agrees that consumers shouldn't necessarily be swayed by claims of high counts of beneficial organisms in their food. "You hear about billions and trillions and how they are better than millions, but there is no data to support most of those claims. Probiotics may be part of a healthy diet, but be skeptical of their impact in formulations that have not been formally tested," he advises.
So what is a cautious consumer to do? Both Quigley and Reid suggest taking a look at the Clinical Guide to Probiotic Products Available in the US; the 2016 version was just released (a separate guide is available for Canada here). The guide reviews indications, dosages, and clinical evidence to date for dozens of common organisms and strains. "This guide lets you know which organisms have been documented sufficiently to be recommended," says Reid.
If that sounds like a lot of work, just keep it simple, Reid says. He recommends sticking to the strains and simple foods that have stood the test of time and science.
After all, humans have evolved and thrived for many thousands of years noshing on fermented foods — from kimchi to natto, kefir to kombucha, miso to yogurt to tempeh. "We should all be eating kefirs, yogurts and sauerkraut," says Reid. "Their lactic acid bacteria are good for us."
Jill Neimark is an Atlanta-based writer whose work has been featured in Discover, Scientific American, Science, Nautilus, Aeon, Psychology Today and The New York Times.