Sleep deprivation may boost levels of a chemical that makes eating more pleasurable, leading to overeating and poor food choices, according to a new study.
Sleep-deprived participants were unable to resist "highly palatable, rewarding snacks," such as cookies, candy and chips, even when they had consumed a meal that supplied 90 per cent of their daily caloric needs two hours before, researchers said.
The effects of sleep loss on appetite were most powerful in the late afternoon and early evening, times when snacking has been linked to weight gain, researchers said.
Researchers from the University of Chicago in the US recruited 14 healthy men and women in their 20s as volunteers.
They monitored the subjects' hunger and eating habits in two situations - one four-day period during which they spent 8.5 hours in bed each night (averaging 7.5 hours of sleep), and another four-day period when they spent only 4.5 hours in bed (4.2 hours asleep).
The participants ate identical meals three times a day, at 9 AM, 2 PM and 7 PM. Researchers measured levels of the hormone ghrelin, which boosts appetite, and leptin, which signals fullness, in their blood.
"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 from 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," said Hanlon.
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, researchers said.
For the first time, researchers measured blood levels of endocannabinoids. After a normal night's sleep, 2-AG levels were low in the morning. They peaked in the early afternoon, soon after lunchtime, then decreased.
After restricted sleep, however, 2-AG levels rose to levels about 33 per cent higher than those seen after normal sleep. They also peaked about 90 minutes later, at 2 PM and remained elevated until about 9 PM.
After the fourth night of restricted sleep, subjects were offered an array of snack foods. Despite having eaten a large meal less than two hours before being offered snacks, subjects in the restricted sleep phase of the study had trouble limiting their snack consumption.
They chose foods that provided 50 per cent more calories, including twice the amount of fat, as when they were completing the normal sleep phase.
This increase in circulating endocannabinoid levels, "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," researchers said.