If you're trying to lose weight, you may have more to worry about than what you eat, or how much exercise you get, according to a new study.
Researchers from the University of Chicago and the University of Wisconsin-Madison have found that not getting enough sleep may sabotage weight loss efforts because of an association between less sleep and an decrease in fat loss.
The study, published in the latest issue of Annals of Internal Medicine, assigned 10 overweight or obese participants to two groups – one that got 5.5 hours of sleep and another that got 8.5 hours of sleep over two periods, each lasting 14 days. All participants were given the same caloric intake and activity regimens. At the end of the study, researchers found while all subjects lost the same amount of weight, the ones who got less sleep lost less fat and more muscle than the group which got more sleep.
"The loss of lean body mass is an unwanted side-effect of all weight loss diets. This side effect was increased by sleep reduction in our study," said Dr. Plamen Penev, one of the study's authors and an assistant professor of medicine at the University of Chicago Medical Center.
Other sleep and weight loss experts say the study's findings are very significant, since few studies have looked at the relationship between sleep deprivation and metabolism. A study like this one, experts say, adds to the growing body of knowledge on the negative impact of not getting enough sleep. They also say the small size of the study is typical of research that carefully monitors sleep and metabolic processes.
"It suggests that short sleep may confer some negative metabolic consequences," said Gary Foster, director of Temple University's Center for Obesity Research and Education, in Philadelphia, Pa.
In addition to decreased fat loss, the findings suggest that limited sleep may affect levels of two hunger-related hormones, ghrelin and leptin.
"It seems that it's mainly the disregulation in leptin and ghrelin that are driving this," said Dr. Reena Mehra, medical director of the Adult Sleep Lab at University Hospitals Case Medical Center in Cleveland, Ohio.
"The longer you're awake, the hungrier you get," said Dr. Nancy Collop, professor of medicine and director of the Emory Sleep Center in Atlanta, Ga.
Sleep deprivation may also play a role in how the body gets its energy.
"It seems like all this kind of suggests that when people are sleep-deprived, their metabolism changes and breaks down different sources of energy," said Collop. Those sources of energy tend to be carbohydrates and protein rather than fat."
"When you're getting less than 7 to 8 hours of sleep, it may affect metabolism and insulin resistance," said Mehra.
Decreased insulin resistance over a long period of time can potentially lead to diabetes, the experts said.
While they agree that the findings are compelling, sleep and weight loss specialists say that a study with only 10 subjects makes it hard to pinpoint exact causes for decreased fat loss. Nonetheless, they say the study emphasizes how important it is to get a good night's sleep.
"It shows us that we ought to be thinking about ways to incorporate sleep hygiene into standard weight control programs," said Foster.