Losing weight can be described at its simplest as a matter of counting calories during the daytime. Consume fewer calories and burn more through activity and exercise, and you’re likely to lose weight. Eat more high-calorie foods and sit on the couch all day watching football, and you get the opposite effect. But according to a new study from University of Chicago Medical Center researchers, another number should be taken into account by dieters: hours of sleep.
Given people generally do not eat or exercise while asleep (aside from some Ambien users), the link between weight and sleep may seem unlikely. But previous research at the University of Chicago found that sleep loss can wreak havoc with a person’s endocrine system, the hormones that control appetite and metabolism. In a 2004 study, men limited to only four hours of sleep a night reported increased appetite and showed hormonal changes consistent with increased hunger – increased ghrelin, which signals hunger, and decreased leptin, which signals satiety. But the long-term influence of those sleep pattern changes on weight gain or loss remained to be studied.
Monday, an experiment testing that connection was published by Plamen Penev, assistant professor of medicine, and colleagues in the Annals of Internal Medicine. And this was no easy experiment: 10 subjects had to spend two 14-day periods essentially living in a laboratory, so that scientists could control their diet, their daily activity, and the amount of sleep. But the small study reached a compelling, unexpected conclusion.
On the surface, the results may look disappointing. Subjects were allowed 8-1/2 hours in bed during one two-week period, and limited to 5-1/2 hours in bed the other two weeks. Diet and exercise were kept the same between the two periods, so that the effect of sleep alone could be isolated. But when the researchers looked at weight loss during the two periods, it was almost identical. Subjects lost about 3 kilograms, or 6 pounds, over the two weeks, whether they were getting a long night’s sleep or the reduced amount.
But not all weight loss is created equal. When the researchers looked more closely at what kind of weight was lost over the two-week periods, an important difference was revealed. With adequate sleep time, more than half of what was lost was fat. But when sleep was limited to less than 5-1/2 hours, only a quarter of the lost weight was due to reduced fat, suggesting that important protein and muscle were being shed instead of unsightly flab.
“If your goal is to lose fat, skipping sleep is like poking sticks in your bicycle wheels,” Penev said. “Cutting back on sleep, a behavior that is ubiquitous in modern society, appears to compromise efforts to lose fat through dieting. In our study it reduced fat loss by 55 percent.”
Why would losing sleep mean a less efficient diet? The sleep-deprived brain may send different signals to its body; ghrelin levels were again increased in this study, and plasma levels of adrenaline were decreased after the shorter sleep period. The resting metabolic rate was also lower in subjects when they slept less, despite the longer time spent awake. Faced with providing energy for 19 hours of wakefulness instead of 16, the body may resort to breaking down muscle for energy instead of fat, the authors hypothesize – like burning a log instead of newspaper.
This phenomenon could connect the rising obesity rates with the decline in average sleep duration in our society. Alternatively, the connection between sleep loss and weight loss could explain why counting calories doesn’t always work for some people, or contribute to the observed sleep difficulties in overweight or obese people. Regardless, it appears that a full night’s rest should be considered a part of any healthy diet.
“The barriers to maintaining healthy body weight are complex and include physiologic, psychological, and social factors” write Shahrad Taheri and Emmanuel Mignot in an editorial accompanying the Annals study. “Perhaps sleep should be included as part of the lifestyle package that traditionally has focused on diet and exercise.”
Nedeltcheva AV, Kilkus JM, Imperial J, Schoeller DA, & Penev PD (2010). Insufficient sleep undermines dietary efforts to reduce adiposity. Annals of internal medicine, 153 (7), 435-41 PMID: 20921542