Scientists have taken another big step in understanding why sleep deprivation can lead to weight gain.
At an annual meeting hosted by the American Academy of Sleep Medicine and Sleep Research Society, scientists presented two studies that used brain imaging to show how a lack of sleep can affect neuronal responses and make it harder for people to chose healthy food options.
"In general, we know that losing sleep impairs decision making, and we know that it impairs metabolism. What these studies show is that they're not two totally separate things," said Michael Grandner, who was not involved in the studies, but works as a research associate at the Center for Sleep and Circadian Neurobiology, part of University of Pennsylvania's Perelman School of Medicine.
In one study from the University of California, Berkley, researchers used MRI scans to monitor 16 adults who rated their desire for 80 foods after a normal night of sleep and after being awake for 24 hours.
The images revealed that sleep deprivation affects areas of the brain that help us sort through and weigh the many factors -- from how good food tastes to how healthy it is -- that influence our decision to eat a certain food.
"For a number of years now, we've started to realize that there's a potential link between sleep loss and obesity," said Matt Walker, an associate professor of psychology and principal investigator at UC Berkley's Sleep and Neuroimaging Lab. He said that to date, much of that research has focused on what is happening or failing in the body, such as changes in the hormones that influence hunger and satiety.
"What we're finding is that there are not only differences that occur in the body in terms of metabolism and hormones, but also a failure in the brain," Walker said. "It's a failure in the ability to integrate signals that help you make appropriate food choices."
In a separate but similar study out of New York, researchers used MRIs to track responses to images of unhealthy foods (like candy and pizza) and healthy foods (like fruits and vegetables) after several nights of just four hours of sleep. They compared those results to the participants' responses after getting a full night of sleep.
The images revealed that when participants only got a few hours of sleep, they had increased activation in the parts of the brain associated with reward and motivation. But when they got plenty of sleep, there were no substantial changes in the brain's activity patterns, suggesting that sleep deprivation may result in increased susceptibility to unhealthy foods -- as well as poor decision making.
"What's interesting is that these two studies overlap. You have two different groups, on two different coasts finding essentially the same thing, which is good," Grandner said.
He pointed out that the study's do have limitations -- chief among them, their small sample size. He said future research would hopefully include more patients and compare people who are overweight and obese with those who aren't.
Overall, the research could help provide a better, more nuanced understanding of how sleep affects weight and general well-being."Sleep is a very important aspect of health. We think a lot about how our diet affects health, and how physical activity affects our health, but we tend not to think about how sleep affects our health," Grandner said. "Hopefully these types of studies will help change that perspective."