Eve Van Cauter, an endocrinologist at the University of Chicago, began untangling the connection between sleep deprivation, diabetes, and obesity more than a decade ago. This year her team discovered that sleep deprivation impedes the metabolism of glucose, the sugar that powers the body, in fat cells by a startling 30 percent. Lack of sleep affects appetite, too: A 2012 Swedish brain-scan study identified heightened activity in the right anterior cingulate cortex—a brain region associated with hunger control—in the sleep-deprived.