Taking a single yoga class can help you lower levels of cortisol, a stress hormone linked to increased belly fat and, ultimately, an increased risk of diabetes and heart disease.

Researchers at Jefferson Medical College took blood samples from 16 healthy yoga novices during a week when they took a daily 50-minute traditional class. The results: Cortisol levels dropped immediately—as soon as the first day. "This is very significant, because there's a vast amount of literature on how stress increases cortisol levels, but little is known about how to bring them down," says neuroscientist George Brainard, PhD, associate academic director of the school's Center for Integrative Medicine.

More research is needed to determine how long the effect lasts and how much yoga will give you optimum benefits. But if you're feeling the effects of stress, yoga is a good way to relax and possibly avoid the health problems linked to chronically high cortisol.