The Master Cleanse trend

Illustration: David Wyffels

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The Master Cleanse

The Idea: Originally launched in the 1940s, this 10-day cleanse enjoyed a celebrity-fueled revival starting around 2006. The gist: Consume nothing but a mixture of water, lemon juice, cayenne pepper and maple syrup (plus a few cups of salted water in the morning and a lovely pre-bed laxative at night) and you'd lose major weight, reset your digestive tract and flush toxins and waste out of your body.

The Problem: First, the claim of getting rid of so-called toxins. Experts agree that there's no scientific evidence behind it—for this or any other cleanse—plus, your kidneys and liver do a fine job of clearing out waste. Second, it's the definition of a deprivation diet. "You're starving yourself, and you'll gain the weight back when you start eating real food," Scritchfield says. "You're also stopping your digestive system in its tracks because there's no fiber, so expect to be constipated." And with little to no protein in the plan, you're losing muscle mass in the process, says Aronne.

The Lesson: If you want to lose weight and keep it off, the formula is simple: move more, eat less (while still eating actual food).