Does your appetite change when you're tired? If you're short on sleep, do you find yourself craving junk food and sweets? Turns out, this dynamic isn't just in your head. But it is in your brain.
We talk a lot about the connection between sleep and weight. An overwhelming body of research has established the links between lack of sleep and weight gain. Large-scale studies show that a routine of sleeping too little makes us more likely to put on weight over time. Lack of sleep has been linked to both increased calorie consumption and to reduced energy expenditure -- that means more calories in and fewer calories out. Sleep deprivation is also associated with disruptions to hormones in the body that regulate appetite. In the past several decades, we've seen obesity rates skyrocket. At the same time, rates of sleep deprivation have also risen dramatically. Nearly a third of working adults are sleeping no more than six hours a night. As a society, we sleep significantly less -- and we weigh a great deal more.
New research now offers some important insight into the underlying connection between lack of sleep and weight gain -- specifically, how sleep deprivation can alter brain behavior in ways that make it more difficult to eat well and keep weight off.
Researchers at the University of California Berkeley examined how sleep affects brain functions that are related to food choices and desire. They found sleep deprivation led to important changes to activity in two very different areas of the brain, both of which help govern eating. The result? After a single night of sleep deprivation, participants' brains responded with greater desire for unhealthy foods than when they were rested. At the same time, their sleep-deprived brains showed indications of diminished capacity to make reasoned, thoughtful decisions that could override the impulse to eat poorly.
Researchers studied 23 healthy adults under different sleep conditions. The group spent two nights in a sleep laboratory. On one night, they slept approximately eight hours and woke to have a light breakfast. After a period of about a week, the participants returned to the laboratory for another overnight session. This time, instead of getting a full night's sleep, participants were kept awake for the duration of the night. They were given snacks throughout the night to compensate for any additional calories they might expend by staying awake. After each night, participants were shown a series of images of a wide variety of foods, from healthy choices like fruits and vegetables to high-calorie foods like potato chips, pizza and dessert. They were asked to rate their desire for each food. As an incentive, researchers told participants they could have the food they rated the highest. While participants were viewing and rating food images, researchers observed their brain function using MRI technology. When they compared the well-rested sessions to the sleep-deprived sessions, they found significant differences in levels of desire for certain foods -- and corresponding differences brain activity:
- When sleep-deprived, people showed greater desire for unhealthful, high-calorie foods, rating these foods more highly than when they were rested.
- Their desire for junk food increased along with the severity of their sleep deprivation. The more sleep-deprived people were, the more they wanted junk food.
- MRI scans showed that when sleep deprived, the "reward center" of the brain responded more strongly to images of high-calorie foods. Specifically, activity increased in the amygdala, a cluster of cells within the brain's temporal lobe that plays a critical role in appetite and desire for food.
- MRI scans also showed significant decrease in activity in parts of the brain's frontal lobe after a night of sleep deprivation. This area of the brain includes mechanisms that govern complex decision-making and behavioral control. When functioning at normal levels, these regions can exert a restraining influence to counterbalance the reward-seeking areas of the brain. Diminished activity results in a brain less able to extend that thoughtful, moderating influence over food decisions.
These results show that the impact of sleep on the brain is twofold: A single night of sleep deprivation makes fattening, high-calorie foods more attractive and at the same time interferes with the brain's ability to override desire with rational decision making.
This isn't the first evidence we've seen that lack of sleep interferes with normal brain behavior regarding appetite, desire, and decision-making about food. Researchers at St. Luke's Roosevelt Hospital Center and Columbia University in New York also used MRI to investigate the impact of sleep on the brain's response to food. Twenty-five men and women were shown images of healthful and unhealthful foods after five nights of normal sleep and again after five nights of sleeping no more than four hours per night. Brain scans revealed a spike in activity in the reward center of the brain when participants viewed unhealthy foods after restricted sleep. No such similar spike occurred when the subjects viewed healthful foods, even after sleeping only five hours per night.
This latest study gives an even clearer picture of just how significant an impact sleep can have on the brain and how those neurological changes may ultimately contribute to weight gain. We know that sleep is an important tool in weight management. These results indicate that getting enough sleep can help prime your brain to help you win the battle against weight gain.
Michael J. Breus, PhD
The Sleep Doctor®
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