Many people who lose weight after dieting often get frustrated when those extra pounds come back. Research suggests that a rise in appetite-stimulating hormones could be to blame. Patients in one study were asked to rate their levels of hunger more than a year after dieting. But Gary Foster, director of Temple's Center for Obesity Research and Education, says since those findings are subjective, it can be difficult to draw lasting conclusions. "Hunger can mean different things to different people," he said. "Hunger isn't the driving force for most people who overeat."