Some people claim they can get by with little sleep. But while they may not have decreased alertness and cognitive ability, a lack of shut-eye has a harmful effect on the body's energy metabolism and can lead to weight gain, diabetes and other health problems over time, say University of Chicago Medicine researchers. In the study, published in today's issue of Annals of Internal Medicine, seven young, lean and healthy volunteers had four straight nights of 8½ hours of sleep, and at least four weeks later had four straight nights of 4½ hours of sleep. Food intake, strictly controlled, was identical during both stints. The four nights of short sleep negatively affected fat cells, reducing by 30 per cent their ability to respond to insulin, a hormone that regulates energy. This reduction is comparable to the difference between cells from obese versus lean participants, or from people with diabetes versus non-diabetic controls.