"Sleep dieting" uses old wisdom to help you amp up your weight loss hormones while you snooze—but is it legit?

By Charlotte Hilton Andersen
March 29, 2016
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Losing weight in your sleep sounds like a dream, right? But some experts are now saying you can make that dream a reality by timing your meals to coincide with natural fluctuations in your hormones at night. (Find out The Strange Way Lack of Sleep Could Be Making You Gain Weight.)

The science of "sleep dieting" all boils down to one word: fasting. All you have to do is stop eating after dinner and not eat again until breakfast, giving your body a 12-hour rest from food. Add that to sleep's proven powers to lower stress hormones and you get a powerful weight loss combo, according to Jason Fung, M.D., a Toronto-based nephrologist and author of The Obesity Code: Unlocking the Secrets of Weight Loss. "Stubborn, diet-resistant weight gain isn't about eating too much or exercising too little; it's not about excess calories or saturated fat. It is, in fact, a complex hormonal issue," Fung wrote in an essay for The Daily Mail.

The first thing you should know is that this isn't new at all; it's actually one of the oldest tricks in the book. "Sleep dieting" is really just another name for intermittent fasting-a diet trend we've been hearing about for a while, thanks to the growing popularity of fasting-based diets like the 5:2 Diet, Leangains, Eat Stop Eat, and Warrior Diet, not to mention that fasting is a key component of CrossFit and Paleo communities. And the practice of abstaining from food for a period of time longer than six hours has been around as long as there have been people. (Although it was not so much a choice as a survival technique for our ancestors.) That led our bodies to make some interesting adaptations to protect us against times when food is scarce, such as allowing us to burn fat during lean times while sparing valuable muscle and bone. (Can Intermittent Fasting Help You Lose Belly Fat?)

But is combination of intermittent fasting and sleep just another diet gimmick, or can it really work? It's true that sleep greatly impacts how your hormones work and can affect your ability to lose weight, says Peter LePort, M.D., the medical director of the MemorialCare Center for Obesity at Orange Coast Memorial Medical Center in Fountain Valley, CA. (In fact, Sleep Is the No. 1 Most Important Thing for a Better Body.)

"I think this is a good strategy to lose weight without feeling deprived or suffering," LePort says of Fung's philosophy. "It allows you to have full meals, eating what you like, but overall you're still eating less."

And let's be honest, when was the last time you were eating salad at 10 p.m.? Usually, late-night snacks are junk food or treats that we add on top of the food we ate earlier in the day. (Why Is It So Hard to Resist Junk Food After Dark?!) LePort adds that fasting overnight also helps reset our hunger cues, helping to stop us from eating too quickly or overeating. If you're worried about the health effects, LePort has good news there too, saying it's perfectly safe for most people to go 12 hours without eating.

"In the end, it's about getting people to eat less, so if fasting helps you stick to your diet then you have a diet that works," LePort says. And if we can do it in our sleep? Even better!