For exclusive access to all our stories, including sequences, teacher tips, video classes, and more, join Outside+ today.
The research on probiotics—good bacteria in your microbiome that fight germs, break down food, and play a role in nutrient and vitamin absorption—is still in its infancy, says Diane McKay, PhD, an assistant professor at the Friedman School of Nutrition Science and Policy at Tufts University. Ideally, your diet alone will support a healthy microbiome: Plenty of whole and fiber-rich foods contain prebiotics—non-digestible plant fibers that nourish beneficial microorganisms in the intestines—and thus improve the good-to-bad bacteria ratio in the body.
However, most Americans don’t get enough fiber, and our increased use of antibiotics may reduce the number of friendly bugs in our systems. So far, only a few probiotic strains have been shown to help certain conditions. Controlled trials have demonstrated that Lactobacillus GG and Saccharomyces (yeast) can shorten a bout of diarrhea in certain cases. And several studies found that Bifidobacterium, Lactobacillus, or Bifidobacterium infantis helped calm irritable bowel symptoms, including bloating and abdominal pain.