Why Sleep Deprivation May Lead to Overeating

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If traditional weight-loss diets have failed you, you might just try hitting the sack.

Growing evidence has linked healthy weight with getting adequate sleep, and in a new report presented at the American Heart Association’s annual Epidemiology and Prevention/Nutrition, Physical Activity and Metabolism conference, researchers found that sleep deprivation is associated with overeating. In the study, people who were sleep deprived ate more than 500 additional calories daily.

That’s a lot of calories. It doesn’t take a mathematician to figure out that over time, the excess consumption can translate into unwanted pounds — though the current study was small and short-term and did not measure participants’ long-term changes in weight.

The study’s lead author, Virend Somers, a professor of medicine at the Mayo Clinic, studied 17 healthy but sedentary men and women in a lab clinic for 11 days and nights. The participants agreed to spend the entire study period at the facility, where researchers recorded their every movement, through a special monitor the participants wore, and tallied everything they ate, either from a cupboard in their room or food they ordered. That way, Somers and his team could make relatively accurate calculations of how much energy the participants were taking in in the form of calories and how much they were burning off through activities like walking.

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After a three-day baseline period, one group was randomly assigned to sleep and wake whenever they wanted for eight days, while another was intentionally woken up after only two-thirds of their usual sleep time — that amounted to about 80 minutes less sleep per night on average. The group that experienced such restricted sleep tended to eat more the following day, adding 549 extra calories to their usual diet, while those who slept as much as they wanted ate about the same on each of the eight experiment days as they did during the three-day baseline period.

The poorly sleeping group was likely to be vulnerable to weight gain over the long term, if their sleep was continually restricted, says Somers, since they did not burn any more calories than their better sleeping counterparts. That may help explain why previous studies have found that shift workers who work at night and sleep during the day tend to gain more weight than day workers: their disturbed sleep pattern may prompt them to eat more while they don’t expend any more energy to work off the added calories.

But what links poor sleep to an increased appetite? “From a physiologic perspective, we know that sleep is a very important time for the release of many physiologic hormones,” says Somers. “It’s a time when the body repairs itself, the brain consolidates memories, and growth hormone is released. All of these important functions are impacted by less sleep time.” And that includes levels of hormones involved in appetite.

But although a reduction in the hormone leptin might seem like the most obvious culprit — leptin is the appetite-suppressing hormone that is released by fat cells at night — in the study, leptin levels in the sleep-restricted didn’t go down. They went up instead. Why that was so wasn’t clear, but Somers theorizes that it was because the participants were gaining weight, and therefore fat, during the study. The added fat cells may have contributed to a spike in leptin production. But Somers did not measure fat changes during the trial, so additional studies will need to be done to confirm his theory.

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Regardless of why sleep loss contributes to weight gain, Somers says it’s important for people to start appreciating that the two are intertwined. It’s also important to remember that the relationship between sleep, eating and weight is a complex one. Getting a consistent and sufficient amount of sleep each night may play an important role in regulating how much we eat and how many calories we burn, and it may also help determine when we eat. Eating when we should be sleeping, for example, may increase the risk of weight gain, as the body is more likely to turn nighttime calories into fat rather than burning them off.

“The magnitude of the effect — the fact that cutting down on sleep by a couple of hours a night over the course of a week or so can make you eat an average of 550 more calories a day — that’s the valuable message from this study,” says Somers. “That’s a lot of extra calories.”

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.

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