The high rate of people regaining weight after dieting is due to hormonal changes, according to a study just released by the New England Journal of Medicine.The study, published on October 27, measured 50 participants' hormone levels before, during, and after a 10-week diet. They were then allowed to resume eating normally, but were given periodic advice from a dietitian and were encouraged to regularly exercise for at least 30 minutes. Following the diet, participants reported feeling hungrier than before and a year later had gained, on average, at least half the weight that had been lost.It was found that dieting leads our appetite-stimulating hormone, Ghrelin to increase significantly from its base level, while the appetite-suppressing, metabolism-boosting hormone, Leptin decreases significantly. These hormonal changes persist even a year after the intitial weight-loss, compelling people to eat more and regain lost weight."Maintaining weight loss may be more difficult than losing weight," lead researcher Joseph Proietto, PhD, a professor of medicine at the University of Melbourne's Heidelberg Repatriation Hospital, told CNN. "This may be due to biological changes rather than [a] voluntary return to old habits."The study findings support the concept that the body strongly resists any attempts to drop below its natural set-point.The hormone changes revealed by the study explain the tendancy for weight relapses, however Proietto says, will power may also play a role in an individual's ability to manage the effects."This may explain why some people maintain weight loss for longer than others," he says. "Maintenance of weight loss requires continued vigilance and conscious effort to resist hunger."Researchers say that further study is needed to find long-term, safe treatments to counteract the hormonal change and prevent relapse, particularly for obese people.