The study also found that when shortened sleep alters the chemical — known as endocannabinoid 2-arachidonoylglycerol, or 2-AG for short — people tend to become unable to resist “highly palatable rewarding food,” such as cookies, potato chips and candy, particularly in late afternoon and early evening.
That’s the time of day when 2-AG appears to peak in sleep-deprived people. It’s also the time of day when snacking has been linked to weight gain.
These findings may help explain the association, observed in many epidemiological studies, between inadequate sleep and overeating, increased body weight and obesity, say the study’s authors.
“We found that sleep restriction boosts a signal that may increase the hedonic aspect of food intake, the pleasure and satisfaction gained from eating,” said Erin Hanlon, the study’s lead author and a research associate in endocrinology, diabetes and metabolism at the University of Chicago, in a released statement. “Sleep restriction seems to augment the endocannabinoid system, the same system targeted by the active ingredient of marijuana, to enhance the desire for food intake.”
For the small but tightly controlled study, Hanlan and her colleagues recruited 14 healthy, non-obese men and women in their 20s. The participants twice made four-day visits to a research lab, where their sleep and food intake was carefully controlled.
During the first visit, the participants spent 8.5 hours in bed, averaging 7.5 hours of sleep per night. During the second visit, they were restricted to 4.5 hours in bed, for an average of 4.2 hours of sleep per night. During each visit, they were fed identical meals at 9 a.m., 2 p.m., and 7 p.m.
Hanlan and her colleagues periodically measured the participants’ blood levels of several chemicals during the days they were in the lab. The chemicals included ghrelin, which tells the brain the body is hungry, and leptin, which signals to the brain that the body is full. In previous studies, high levels of ghrelin and low levels of leptin have been associated with lack of sleep and increased appetite.
The researchers also measured — for the first time, they say — blood levels of endocannobinoids. And it was these measurements that revealed a fascinating pattern.
When the participants got a normal night’s sleep, 2-AG was low in the morning, peaked around 12:30 p.m., and then fell throughout the rest of the afternoon and evening. When the participants’ sleep was restricted, however, this pattern changed. First, the levels of 2-AG were about 33 percent higher. In addition, the levels peaked later in the afternoon — around 2 p.m. — and remained elevated until about 9 p.m.
The study also found that when the participants were sleep-deprived, they reported being much hungrier and eager to eat, particularly after their second meal of the day — which was also when their 2-AG levels were highest.
After the fourth night in the research lab, participants were given unlimited access to snacks in the late afternoon. They were much more likely to consume these foods when sleep deprived — even though they had finished their lunch just two hours earlier.
The participants were also more likely to reach for “junk food” snacks when sleep deprived, taking in an average of 50 percent more calories and twice the amount of fat as they had when offered snacks when not sleep deprived.
Limitations and implications
This study has several limitations. It involved, for example, only a small group of people with similar characteristics, such as age and weight. The results, therefore, may not apply to other populations. In addition, the participants were followed for only a short period of time.
Still, the findings are provocative and support other research that suggests getting a good night’s sleep can be an important aid in maintaining a healthy weight.
“If you have a Snickers bar, and you’ve had enough sleep, you can control your natural response,” said Hanlon. “But if you’re sleep-deprived, your hedonic drive for certain foods gets stronger, and your ability to resist them may be impaired. So you are more likely to eat it. Do that again and again, and you pack on the pounds.”
FMI: Despite being funded in part by the Department of Defense, the full study is behind a paywall, but you’ll find an abstract on the Sleep website.