Scientists may have pinpointed the reason why food looks so good after a bad night's sleep.
Researchers from the University of Chicago found that when healthy, young adults who were not obese slept for just four-and-a-half hours during the night, they had higher blood levels of a molecule called 2-arachidonoylglycerol, which regulates the feelings of "reward" and enjoyment from eating, compared with their peers who got eight-and-a-half hours of sleep.
"Past experimental studies show that sleep restriction increases hunger and appetite," study researcher Erin Hanlon, Ph.D., who is a research associate at the University of Chicago's Section of Endocrinology, Diabetes and Metabolism, said in a statement. "The mechanism for overeating after inadequate sleep may be an elevation in this endocannabinoid molecule, called 2-arachidonoylglycerol, or 2-AG."
Researchers noted that this finding could improve understanding for why obesity and being overweight are linked with sleep deprivation.
The new study was presented at the annual meeting of The Endocrine Society; because it has yet to be published in a peer-reviewed journal, its results should be regarded as preliminary.
The study included nine people, age 23 on average, who spent two six-night stays in a sleep lab a month apart. For one of the six-night stays, participants slept from 11 p.m. to 7:30 a.m. -- an 8.5-hour sleep time, which is supposed to be indicative of "normal" sleep. For the other six-night stay, participants slept from 1 a.m. to 5:30 a.m. -- a 4.5-hour sleep time, supposed to be indicative of sleep deprivation. In the daytime hours, all the study participant ate controlled amounts of calories.
Researchers took blood sample from the participants after the second night of each of the six-night stays, to determine their levels of 2-arachidonoylglycerol. Levels of this molecule were found to typically be lowest halfway through a person's sleep time, but highest in early afternoon. But after a period of short sleep, researchers found that the levels of 2-arachidonoylglycerol were even higher than normal in the early afternoon.
2-arachidonoylglycerol isn't the only molecule that seems to be upped after bad sleep -- a recent study presented at the annual meeting of the Society for the Study of Ingestive Behavior showed that the hunger hormone ghrelin is found at higher levels in the blood after a night of disrupted sleep, not to mention greater feelings of hunger. A similar conclusion was reached in a Journal of the Academy of Nutrition and Dietetics review published last year.
Plus, a study published earlier this year in the journal Psychoneuroendocrinology showed that after a night of sleep deprivation, people tend to want bigger portions of food.