The eternal question: If you snooze, do you really lose? For years now, a flurry of research studies has linked inadequate sleep and weight gain, giving us all an excuse to hit the snooze button. Then in 2013, a new study seemed to contradict the earlier findings. So what is the truth? 

The short answer: If you want to lose pounds or are in healthy-maintenance mode, getting enough sleep is a must. “It is critical to understand that sleep has an impact on our weight,” says Carol Ash, DO, Director of Sleep Medicine at Meridian Health in New Jersey. 

The real question is why. Some of the reason has to do with the body’s hunger hormones. One, the impish-sounding ghrelin (if you first read “gremlin,” so did we) is released mainly by the stomach and signals to the brain, “I’m hungry.” Another, leptin, is manufactured in fat cells. It tells the brain when the body has enough stored energy to go about its business—essentially, “OK, put down the fork; I’m satisfied.” The two work in combination with other biochemicals to regulate the appetite.  

In the early 2000s, researchers looked closely at the Wisconsin Sleep Cohort Study, a massive, ongoing academic survey of Americans’ snoozing habits that began in 1989. Experts noted a link between sleeping time and hunger hormones. Subjects who logged 5 hours on average were found to have less leptin and more ghrelin in their systems than those who averaged 8 hours. In other words, the short sleepers had too much of the “feed me” signal and not enough of the “stop” signal. They also had a higher average percentage of body fat.   

The cause-and-effect between getting less sleep and gaining weight seemed pretty obvious, until the University of Colorado, Boulder, released the results of a highly controlled experiment in 2013. For that study, a group of male and female subjects lived for 2 weeks in a laboratory. Their sleep was strictly controlled, but they were allowed to eat whatever and whenever they wanted. The results seemed to contradict earlier studies. The people whose sleep was restricted to 5 hours a night were actually found to have reasonably normal amounts of ghrelin and leptin in their systems. And they burned about 100 calories a day more than did their better-rested counterparts.      

But the overall results of the experiment still support the original premise: Not enough sleep can make you fat. It turns out that the short sleepers still ate more than the well-rested subjects did. And even with their slightly speedier metabolisms, they ended up consuming more calories than they burned off. In the end, subjects gained an average of about 2 pounds each after just a week of sleep deprivation. 

Researchers believe that there was a combination of forces at work, including an exhaustion-induced lack of willpower: The tired people tended to skimp on breakfast, did a lot of late-night snacking and overate carbs. Once they were back to getting enough sleep, they ate less and made healthier choices. 

The bottom line: If you want to be fit and healthy, get to bed on time. “Everyone knows about the benefits of diet, stress-reduction and exercise,” says Ash. “Sleep is the fourth major category of prevention and wellness.” 


  1. Carol Ash
  2. Wisconsin Sleep Cohort Study
  3. Conflicting Study
  4. University of Colorado Study