When to use them: If you have stomach issues regularly. Try taking them daily, via foods or supplements.
What they do: Probiotics are beneficial bacteria that help maintain a healthy digestive tract. (Conversely, antibiotics kill bacteria, both good and bad.) “Probiotics are your friends,” says Weiss. “We’re still not sure why exactly they work, but once people start taking them, many find they feel better.” Dairy products, like yogurt, kefir, and buttermilk, contain different strains of acidophilus, a powerful probiotic. (The probiotics in yogurt have actually been shown to shorten the duration of stomach upset.) You can also find supplements, like Culturelle, and chewable probiotic tablets in health-food stores. Look for Lactobacillus GG, an extensively studied form of acidophilus, or Bifidobacterium bifidum, also believed to be a well-tolerated immunity booster.