Why Darkness Is Crucial for Weight-Loss

Want to lose weight? Turn off the lights. The sleep-promoting hormone melatonin can help your body produce a special kind of calorie-burning fat, according to an animal study recently published in Journal of Pineal Research.

In the study, a team of Spanish and American scientists fed 16 rats diets that were identical except for one difference: Some of the rats drank melatonin-enhanced water, while others drank regular water. At the end of the study, the researchers examined each animal’s body for white and brown fat cells. (A primer: White fat stores calories and leads to weight gain, while brown fat burns way more calories than white fat and promotes weight loss.)

Interestingly, the rats that drank the melatonin-spiked water had more calorie-torching brown fat than white fat—even though their diets didn’t change. Study co-author Russel Reiter, Ph.D., a professor at the University of Texas Department of Cellular and Structural Biology, says that melatonin can spark brown fat production and even turn some white fat into brown fat.  

If these effects translate to humans (and Reiter says he thinks they would), melatonin could be the key to burning more calories without dieting. While previous research suggests that exercise and cold temperatures can trigger brown fat production as well, supplementing these efforts with melatonin is just plain easier—especially because you don’t have to move more or freeze your butt off to see results. What’s more: Melatonin is even safer than most OTC pain-killers, says Reiter. And while it’s typically prescribed to promote sleep, it doesn’t make people super-drowsy like other sleep aids.

Because there haven’t been any human studies yet, though, it’s unclear how much melatonin you’d need to take to see the number on the scale budge. The good news: Your body produces melatonin naturally in response to complete darkness. To boost your body’s melatonin levels, just cut out all light at night: Invest in black-out bedroom shades, trash your nightlight, and keep the bathroom light (and your iPhone and iPad) off until the a.m. And if you’re thinking of taking melatonin supplements to further boost your body’s levels of the hormone, talk to a doctor first to make sure it won’t have any adverse health effects.