Dr. David L. Katz, O, The Oprah Magazine's resident nutrition expert explains the healthy way to fast.
Q. I fast for a day every so often because I like the way it makes me feel. Is that a bad idea? Is there a healthy way to fast? — Anonymous
A. Occasional fasting is fine provided you're in good health. We probably evolved to deal with periodic fasts, given that our ancient ancestors' food supply was so unreliable. There may even be some benefit: Studies tracking Muslims throughout Ramadan—when the devout fast about 12 hours a day for a month—suggest that the practice raises good cholesterol and lowers inflammation of blood vessels. Mormons—who fast one day out of each month—are about 40 percent less likely to have clogged arteries than people who don't fast.
The flip side is that if you're diabetic, fasting can be dangerous, even deadly. For some, it can trigger a rare type of stroke. And don't be fooled by claims that fasting cleanses the body: Healthy intestines, kidneys, and liver do that job for us. Another concern I have about fasting is that it might trigger feasting—the pattern seen in binge-eating disorder.
If you're fasting because it makes you feel good—and you don't overeat afterward—I can't see any real problems, as long as you stay well hydrated. But don't do it more than once every couple of weeks.