Lost sleep can add up to extra weight, according to new research from the Mayo Clinic. In the eight-day study, healthy adults who slept 80 fewer minutes than a control group consumed an average of 549 additional calories daily. Although they were awake longer, their activity level remained stagnant and they didn't burn more calories during those extra hours. So why the spike in appetite? Researchers aren't sure. Previous studies have shown that sleep-deprived people eat more in part because the satiety hormone leptin goes down while the hunger hormone ghrelin goes up--but in this study, researchers saw a trend in the opposite direction, says Andrew D. Calvin, MD, co-investigator cardiology fellow and assistant professor of medicine at Mayo Clinic. The hormonal changes appear to be the result of the increased food consumption, not the cause. Still, Calvin stresses: "If people want to maintain a healthy weight or lose weight, they should try to avoid sleep deprivation."