Widely publicized claims have linked sleep loss to weight gain and obesity. These claims are based primarily on two very small studies conducted by the same researchers on young male adults. They found that, compared to sleeping nine hours a night for one week, sleeping just under four hours a night for a week was associated with hormonal changes that are associated with increased hunger, appetite, and overeating. However, other researchers have failed to replicate these findings and they have not been replicated in women, large samples of subjects, or middle aged and older adults and may not be clinically meaningful. Furthermore, comparing more than nine hours of sleep to just under four hours of sleep is very unrealistic since most people don’t sleep more than nine or less than four hours per night. Additionally, research has not shown a consistent relationship between insomnia and obesity, and massive epidemiologic evidence demonstrates a U-shaped relationship between sleep duration and obesity: long sleep and short sleep are equally associated with obesity. Also, no studies have convincingly demonstrated a cause-and-effect relationship between sleep duration and obesity since it may simply be that people who sleep less use the extra wake time to eat more (particularly if stress is disturbing their sleep since stress may be associated with increased consumption of comfort foods and alcohol) while people who sleep a lot put on weight because they may spend less time exercising.

In the largest and most rigorously controlled study to date on sleep and appetite, a study published in the journal Sleep conducted at Columbia University on men and women failed to find a relationship between short sleep and hormonal changes consistent with increased hunger and appetite. And in another study conducted at the University of Pennsylvania, researchers found that it is the extra hours of wakefulness, and not sleep loss itself, that contributes to weight gain due to increased caloric consumption in late-night hours. In other words, subjects ate more because they spent extra time awake and had more time to eat late at night (perhaps to compensate for increased energy expenditure or boredom from the additional late night awake time) but not because their sleep duration was reduced.

These studies, in conjunction with prior studies finding no relationship between sleep loss and overeating, suggest that media reports and some sleep scientists have misled the public and healthcare professionals about the relationship between sleep and obesity. These exaggerated claims have led to widespread, sensational media claims such as “Sleep more to fight obesity” and “Sleep less, more weight” and misleading books such as “Lose Weight Through Better Sleep”. Such claims, which require a giant leap of faith, suggest that some sleep scientists and the sleep research community have an inherent conflict of interest in promoting the concept that short sleep predisposes to obesity.

In truth, massive epidemiologic data on obesity clearly suggests that we are more likely to lose weight by spending extra time exercising each day or dieting, not by sleeping more. Further, suggesting that we should sleep more to reduce obesity may actually be harmful since too much sleep is associated with increased obesity and increased mortality risk. Recommendations to “get more sleep” may also be dangerous since many people use sleeping pills to gain more sleep, yet sleeping pills have also been consistently associated with increased mortality risk.