What the Yuck: How long is safe for a juice fast?

Too embarrassed to ask your doctor about sex, body quirks, or the latest celeb health fad? In a regular feature and a new book, "What the Yuck?!," Health magazine medical editor Dr. Roshini Raj tackles your most personal and provocative questions. Send 'em to Dr. Raj at whattheyuck@health.com.

Q: How long is it safe to stay on a juice fast?

Don't do it longer than one day. Our bodies need a varied diet—too much of any one food to the exclusion of everything else deprives us of the essential nutrients we need to function well.

Drink only juice and you'll miss out on protein, healthy fats, and a slew of vitamins and minerals. Plus, healthy adults who swear off foods can suffer fatigue, headaches, constipation, and even heart rhythm irregularities. And certain people should never, ever fast (children, pregnant women, people with diabetes, kidney or liver disease, and anyone taking prescription drugs).

The proponents of juice fasting and other detox diets claim your body needs a "break" from digesting solid food in order to detoxify and help reset some sort of balance. As a GI doctor, I can tell you this is absolutely not true. Our kidneys and liver are responsible for removing toxins, and they do not react well to fasting. So that means your fast could actually prevent your body's natural detox system from doing its job. As for your digestive system needing a rest? False.

But let's be honest: The real reason most people try these extreme fasts is to lose weight fast. While you may knock off a couple of quick pounds on a juice bender, you're just losing water weight so those pounds will come right back. And let me tell you, a few days with less bloat is not worth risking potentially dangerous side effects.

Roshini Raj, M.D., is Health magazine’s medical editor and co-author of “What the Yuck?!.” Board-certified in gastroenterology and internal medicine, Raj is also an assistant professor of medicine at New York University Medical Center and a contributor on the “Today” show.

Copyright Health Magazine 2011