Probiotics are having a moment. The tiny buggers are marketed as health enhancers for adults, for kids, and even for dogs (in a beef flavor, of course). You can now pop a capsule, swig a fruit drink or eat an energy bar that's been spiked with probiotics, which the World Health Organization defines as "live microorganisms" that "confer a health benefit on the host" as long as enough of them enter the system.1
The concept of using "good" bacteria to improve health may feel like a recent idea, but it was first put forward by Ilya Metchnikoff, a Russian scientist born in 1845 who thought the colon was a "vestigial cesspool" and hypothesized that the friendly microbes in yogurt might help improve the population of the bacteria in your gut.2 A century after his death, consumers are snapping up the products based on his idea. According to the National Health Interview Survey, 3.9 million U.S. adults reported using probiotics or prebiotics in 2012, the most recent year for which data is available. That was almost 3 million more than in 2007, so it's safe to assume that even more people are taking them now. Sales of probiotics worldwide passed $32 billion in 2013 and are likely to reach $52 billion by 2020, according to Grand View Research.
It's the third day of this week's series on gut science. We've written about whether gut science is biased, why we're so obsessed with constipation, and we've made a video about what poop can tell us about our health — and there's more to come later in the week.
But there is still so much we don't know about whether and how the probiotic products now on the shelves — which most commonly contain bacteria from the Lactobacillus and Bifidobacterium genera — can improve health.3 Probiotic supplements (and to a lesser extent, prebiotics) have been studied for a host of ailments, including digestive problems, allergic disorders, obesity, dental problems, the common cold, high cholesterol and gestational diabetes. But there's limited evidence that they work for any but a handful of conditions. The probiotic craze has gotten ahead of the science.