Gaining weight from overeating is a problem faced by many adults, and now scientists have apparently discovered one reason why.In experiments with rats, researchers found that the hormone leptin, which helps burn fat in fat cells called adipocytes, becomes ineffective, allowing for weight gain from overeating."The cells that make leptin are fat cells -- the cells that store the fat,” said lead researcher Dr. Roger H. Unger, a professor of internal medicine and director of the Touchstone Center for Diabetes Research at the University of Texas Southwestern Medical Center at Dallas.This dichotomy has led to a question that’s only now being answered, Unger said. “Why would cells that have as their main function fat storage produce a hormone that would prevent fat storage by burning up all the fat?” he said. “How is it possible that these cells produce a fat-burning hormone, and yet store a huge amount of fat?"Unger’s team found that when rats are overfed and made obese, the receptor for leptin, which makes fat burn up, disappears from the fat cell. “So the leptin produced by the fat cell will not come back and act on the fat cell,” Unger said. “That way the cell can be smothered by leptin, but the leptin can’t work."There is an evolutionary reason for this, Unger said. “We think of obesity as bad, but in fact throughout evolution, obesity is the only way we survived famine. The people who were most efficient in storing fat were the people who survived,” he said. “Obesity is nature’s way of surviving famine."The new research appears in this week’s online edition of the Proceedings of the National Academy of Sciences.
