COMMENTARY

Sleep Duration Important in Weight Management

Aaron B. Holley, MD

Disclosures

October 18, 2016

Sleep and Body Weight

There is a relationship between sleep restriction and weight gain. In observational studies, as self-reported sleep duration declines, the likelihood of weight gain and obesity increases.[1,2] The onset of the current obesity epidemic is mirrored by a reduction in total sleep time per night at the population level.[3,4]

In 2013, a paper published in the Proceedings of the National Academy of Sciences reported the mechanisms responsible for the link.[5] The authors studied 16 adults for 2 weeks. All participants lived in an experimental laboratory where caloric intake and sleep duration were rigidly monitored and controlled. They were forced to limit their sleep to 5 hours per night for 5 nights, after which they spent several nights catching up at 9 hours of sleep per night.

The researchers found that restricted sleep led to an increase in total energy expenditure. Unfortunately, subjects compensated by upping their caloric intake. There was a net positive energy balance and associated weight gain. Participants also increased the percentage of carbohydrate in their meals. Caloric intake and content offset the effect from prolonged wakefulness and an elevated metabolic rate.

Authors of a recent study published in the journal Sleep tested the inverse of the sleep duration–weight gain relationship.[6] Twelve young-adult males of normal weight were studied in a lab for 5 days. On the second and third days of the experiment, their caloric intake was reduced to 10% of baseline. On the fourth and fifth days, they were able to eat freely without restriction. Sleep was measured each night with polysomnography.

During caloric restriction, the percentage of slow-wave sleep (SWS) increased. Although the researchers didn't measure "delta power," given that most SWS was stage IV, one can infer an increase. Additional relationships between caloric restriction and serum endocrine markers were found: reductions in leptin, thyrotropin, and orexin.

Sleep, Diet, and the Endocrine System

The authors of this study spend time discussing the complex interactions between eating, sleep, and the endocrine system. They also offer an evolutionary theory to explain their findings: Humans adapted to protect themselves from starvation conditions by spending more time with a lower metabolic rate, in SWS. We are not unlike animals who hibernate.[6]

During SWS, the metabolic rate hits its nadir, along with heart rate and blood pressure. Growth hormone is secreted during SWS, arousal threshold increases, breathing stabilizes, and sleep continuity is optimized. The greater the delta power within SWS, the more these changes are assumed to occur. SWS is critical when caloric intake is normal, and now we know that it is even more important when energy balance is negative. The conditions imposed on the study participants (energy intake reduced to 10% of baseline) were much more severe than in most diets. Still, for those trying to achieve a net negative energy balance through dieting, I would consider increasing total sleep time. You're likely to need more SWS than usual.

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