Probiotics are “good” bacteria and they’ve been consumed, in yogurt and other products, for hundreds of years in Europe and Asia to prevent and treat a variety of gastrointestinal ailments. Their popularity in the US is growing as dietary supplements designed to restore a healthful balance between good and bad bacteria in the gut. Restoring this balance can be especially important while you’re taking antibiotics, which kill off good as well as bad bacteria, leaving many people with cramps and diarrhea.