Research has linked obesity with how much sleep you get.

“At least two dozen studies have documented that people tend to weigh more if they sleep less, says Sanjay Patel, M.D., a researcher at Case Western Reserve University in Cleveland. In a 16-year study of almost 70,000 women, Dr. Patel and his colleagues found that those who slept five hours or less a night were 30 percent more likely to gain 30-plus pounds than those who got more rest…

Researchers at the University of Chicago allowed people to sleep five and half hours one night and eight and a half on another, then measured how many free snacks the participants downed the next day. They ate an average of 221 calories more when sleepy—an amount that could translate into almost a pound of fat gained after two weeks! ”

(Via).

The proposed mechanism:

Sleep-deprived animals eat excessively, and humans subject to sleep deprivation show increased appetite and an increased Body Mass Index, the standard measure of excessive weight. The apparent mechanism for this phenomenon is the effect that sleep deprivation has on at least two hormones that influence appetite: leptin and ghrelin. Sleep deprivation causes a decrease in leptin, which boosts appetite and produces obesity, and increases ghrelin, a potent stimulator of hunger and appetite. A study led by J.P. Chaput and published in the International Journal of Obesity this spring found that children who slept an average of 10.5 to 11.5 hours a night were more at risk for obesity than children who slept between 12 and 13 hours a night. Kids who slept only eight to 10 hours a night were at still greater risk. The study had methodological weaknesses (small sample size, data mostly by parental report, absence of correction for age). Still, the trend is striking and suggests that sleep deprivation is associated with obesity in children as well as adults.

– Sydney Spiesel, Slate, Why We’re Fatter.

Of course, sleeping more has lots of other benefits.