Why? “When you eat, there is a natural increase in digestive enzymes and bile salt production as your digestive system prepares to, well, digest your food," explains Gregor Reid, Ph.D., the chief scientist at the probiotic company Seed. Those enzymes and bile salts can kill the bacteria in your probiotics long before they ever get to your small and large intestines, where their real work is done. Taking the supplements when you're not digesting food (and therefore there are lower levels of these substances in your stomach) increases the chances that the bugs will survive their transit intact so they can influence your health. For these reasons, taking your supps after a meal might be a mistake, but before or as you start eating is an optimal window.
Studies back this up. One team of researchers found that the common bacteria Lactobacillus and Bifidobacterium have the best chances of survival when taken up to 30 minutes before a meal. It noted that those taken 30 minutes after munching didn't survive in high numbers.
But most experts agree that consistency is more important than timing. Aim to take your probiotics around the same time every day. "Probiotics are transient microbes,” Reid says. They pass through your colon, benefiting you as they interact with other bacteria along the way, but then ultimately leave your body. So, you need to constantly replenish your supply, he says. "This is why continuous intake is important.”