This may sound a little hard to believe, but if you want to lose weight, turn off your lights and go to bed. Sleep-promoting melatonin can help your body produce some kind of calorie-burning fat, according to an animal study published in the Journal of Pineal Research.

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 the others drank regular water. At the end of the study, researchers examined each animal's body for white and brown fat cells: White fat stores calories and leads to weight gain, while brown fat burns way more calories than white fat and promotes weight loss.

The rats that drank melatonin-spiked water had more calorie-burning brown fat that white fat. 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 worked on humans (and Reiter says he thinks they would), melatonin could be the key to burning more calories without dieting.

But because there haven't been any human studies, it's unclear how much melatonin you'd need to take to see a difference in weight. But the good news is that your body produces melatonin naturally in response to complete darkness.

To boost your melatonin levels, turn off all the lights at night, and invest in black-out bedroom shades.