Daily hormone injections helped dieters keep weight off in a study that helped shed light on why it is so easy to gain weight and so hard to keep it off, researchers said on Thursday.Their study showed that the hormone leptin, useless for helping people lose weight, could help people maintain weight loss -- as long as they got twice-daily injections.The finding helps researchers understand the complex way that human bodies regulate metabolism and put on fat, said Dr. Michael Rosenbaum of the Columbia University College of Physicians and Surgeons in New York."Anybody who has ever lost weight and tried to keep it off knows ... that you never lose as much weight as you think you should. And if you manage to lose as much weight as you’d like to, it’s very, very difficult to keep it off,” Rosenbaum said in a telephone interview.In the 1990s, scientists discovered leptin, a hormone produced by fat cells that caused rats to lose weight when injected. But it failed to have the same results in humans, except for people with a defect in the leptin gene.Other hormones associated with hunger, metabolism and weight, such as neuropeptide Y and ghrelin, have had similarly disappointing results -- indicating that obesity is far more complicated in humans than in rodents.The study of 10 obese and non-obese volunteers showed it is possible to restore leptin levels to a pre-weight-loss point, and in turn keep a dieter’s weight stable."The importance of this is understanding how leptin works. This study was not designed specifically to look at weight reduction therapy,” said Rosenbaum, whose team reported their findings in the Journal of Clinical Investigation.
