Not getting enough sleep has long been tied to overeating, unhealthy food choices and weight gain. Now a new study at the University of Chicago reveals exactly why this happens: Sleep deprivation increases blood levels of a chemical that significantly enhances our joy of eating, particularly snacks that are high in sugar, salt and/or fat.
For the study, the researchers recruited 14 healthy young men and women in their 20s. The participants’ hunger and eating habits were monitored in two situations: one four-day stay in the University’s Clinical Research Center during which they spent 8.5 hours in bed each night (averaging 7.5 hours of sleep), and another four-day stay when they spent only 4.5 hours in bed (4.2 hours asleep).
The researchers found that when the participants were sleep-deprived, they were unable to resist “highly palatable, rewarding snacks,” such as cookies, candy and chips, even though they’d eaten a meal two hours prior that supplied 90 percent of their daily caloric needs. Appetite was most affected in the late afternoon and early evening, times when snacking has been linked to weight gain.
“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, Ph.D., a research associate in endocrinology, diabetes and metabolism at the University of Chicago.
“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.”
This chemical signal is the endocannabinoid 2-arachidonoylglycerol (2-AG). Blood levels of 2-AG are typically low overnight. They slowly rise during the day, peaking in the early afternoon.
When the participants were sleep-deprived, however, endocannabinoid levels rose higher and stayed elevated through the evening, beyond the typical 12:30 p.m. peak. During that period, the sleep-deprived individuals reported feeling hungrier and having a stronger desire to eat. When given access to snacks, they ate nearly twice as much fat as when they had slept for eight hours.
This increase in circulating endocannabinoid levels, the authors note, “could be a mechanism by which recurrent sleep restriction results in excessive food intake, particularly in the form of snacks, despite minimal increases in energy need.”
“The energy costs of staying awake a few extra hours seem to be modest,” said Hanlon. “One study has reported that each added hour of wakefulness uses about 17 extra calories. That adds up to about 70 calories for the four hours of lost sleep. But, given the opportunity, the subjects in this study more than made up for it by bingeing on snacks, taking in more than 300 extra calories. Over time, that can cause significant weight gain.”
While the study had some limitations — small size, short duration, limited sampling frequency — the findings are clearly significant and consistent with the epidemiologic evidence, the authors note. They are also relevant to normal life conditions.
This tells us that “if you have a Snickers bar, and you’ve had enough sleep, you can control your natural response,” Hanlon explained. “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.”
The findings are published in the journal SLEEP.