The correlation between obesity and inadequate sleep has been known for some time.  But does one cause the other or are they coincidental?  It’s also known that inadequate sleep increases hunger, an effect I can attest to from my memories of medical training.  I always ate more than usual on the days following nights spent in the hospital.

So people who don’t sleep enough feel hungrier and presumably eat more than people who get enough sleep.  Is that the only mechanism connecting poor sleep to weight gain?  To answer this question investigators performed a small but fascinating study which was published in the current issue of Annals of Internal Medicine.  Ten overweight sedentary adults spent 14 consecutive days in a sleep lab, where their activity, sleep, and food intake could be continuously monitored.  (Why hasn’t this been made into a reality show?)  They were provided with a calorie-restricted diet containing 90% of their daily metabolic rate.  They had no access to other food.  They were randomized to be allowed to spend either 8.5 hours in bed nightly (normal sleep group) or only 5.5 hours nightly (sleep-deprived group).  Their weight, hunger, percent body fat, and multiple metabolic factors were measured before and after the 14 days.  Several months later the same adults repeated the 14 day stay in the sleep lab, this time in the other sleep group.  They did not engage in any exercise, and just did typical home or office activities.

As expected, the subjects who were being sleep deprived reported greater hunger, but since their diet was controlled, they could not compensate for their hunger by eating more.  Interestingly, subjects lost equal amounts of weight whether sleep deprived or not – an average of 6.6 lb over the 14 days.  That’s over 3 lb per week, which demonstrates the effective weight loss possible in a controlled environment.  Obviously, in the real world people have access to food, and refraining from eating despite hunger is exceedingly difficult.  The dramatic difference was that when the subjects were allowed 8.5 hours of sleep, they lost an average of 3 lb of fat, compared to only 1.3 lb from fat when sleep-deprived.

These findings suggest a few interesting observations.  First, when sleep deprived, most of the lost weight was lean mass, presumably muscle.  That means that the sleep-deprived state switches our metabolism to preferentially burn protein rather than fat, a serious setback for someone trying to lose weight.  Second, even when subjects were sleeping normally, significant lean mass was lost, suggesting that preservation of lean mass when dieting must involve exercise.

So what have we learned?  You’ll definitely lose weight if you don’t have access to as much food as you’d like.  (Ask anyone in North Korea.)  You’ll lose more fat weight if you restrict your calories and get enough sleep.  And if you restrict your calories and don’t exercise you’ll lose almost as much lean mass as fat.

So if you’re overweight, eat less, exercise more, and get enough sleep.

Learn more:

Wall Street Journal Health Blog:  Study: Dieters Foregoing Sleep May Lose Muscle, Not Fat

Annals of Internal Medicine article:  Insufficient Sleep Undermines Dietary Efforts to Reduce Adiposity

Annals of Internal Medicine editorial:  Sleep Well and Stay Slim: Dream or Reality?