At the annual meeting of the Associated Professional Sleep Societies today, Dr. Walter Moraes of Universidad Federal Sao Paolo, Brazil, presented the findings from a study he recently conducted which demonstrated that people lose weight three times as fast while asleep than while lying in bed awake. Dr. Moraes studied 14 healthy men age 21-30, confining them to a bed with a built in scale which allowed him to constantly monitor their weight. The subjects spent the night in bed asleep, and then remained in bed for the next 8 hours, awake. They were given food and drink proportionate to their body weight and, according to the poster, did not urinate or defecate during the study. Dr. Moraes found that the average weight loss during sleep was 1.9 gram/minute (or ¼ pound an hour), but only 0.6 gram/minute while lying in bed awake.

Much has been made recently of the connection between insufficient sleep and weight gain, and this has been explained by changes in the hormones which govern hunger and satiety, leptin and ghrelin. However, this study presents a tantalizing new possibility: that one's metabolism is increased during sleep, leading to more calories burned, and weight loss.

Why might this be? It seems so very counterintuitive at first glance. After all, while sleeping, we seem to be doing less than at any other point in our waking lives. And yet, there are a number of possible explanations. The brain, which comprises only 2% of the body's weight, is responsible for 20% of the body's total energy consumption. We know that in rapid eye sleep (REM), in which we spend roughly 25% of our total sleep time, the brain's metabolic rate (the rate at which it consumes energy) is very high, even more than while awake. And while one's body temperature drops while sleeping, during REM it increases, and this too may cause increased caloric expenditure (as one person discussing this study commented, "it's like a furnace switching on and off across the night").

So it may indeed be that a combination of changes in the hormones leptin and ghrelin, as well as the increased brain metabolism in REM (which is mostly concentrated in the last half to third of the night, so that not getting enough sleep could also result in less time in REM), are what cause us to lose more weight while asleep than awake.

Finally, we know when the best time of day to weigh one's self is, especially when trying to lose weight.

Best,

Dennis

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Dennis Rosen, M.D.

Help your child get a great night’s sleep with my book:

Successful Sleep Strategies for Kids (A Harvard Medical School Guide)

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