Leptin Fading As the Answer to Human ObesityBy
Leptin has become a hot area for obesity research since the
discovery of a mutation in the mouse leptin gene that increases the
animals' appetite while lowering their metabolic rate. New findings,
however, dampen the prospect that this hormone-like signal may explain
differences in body fat among people.
The research was done at the Human
Nutrition Research Center on Aging at Tufts, Boston. The center
is funded by the Agricultural
Research Service, USDAs chief scientific agency.
The researchers found no relationship between the amount of leptin
circulating in the blood of 61 men and women and the total number of
calories they burned each day or their metabolic rate while resting or
after eating. The study volunteers ranged in age from 18 to 81, and
none were obese.
The researchers concluded in the September issue of Obesity
Research that leptin doesn't influence energy regulation in adults
by increasing their energy expenditure. In a study by others, young
children with higher leptin levels reportedly burned more calories
during physical activity. But the recent study indicates adults
apparently lose their responsiveness to this signal.
Maintaining a stable body weight is a matter of burning as many
calories as we consume. In people whose weight control mechanism is
working properly, the body's metabolic rate automatically revs up
after periods of overeating and slows down after periods of
undereating to maintain this balance. Similarly, appetite
automatically adjusts by decreasing or increasing. This process of
energy regulation is controlled by a sequence of metabolic signals.
But the details of that sequence are still sketchy.
To better understand leptin's role, Susan B. Roberts, who heads
energy metabolism studies at the Boston center, and her colleagues
examined how leptin might affect metabolic rate in adults. Because
leptin is produced by fat cells, the volunteers who had more body fat
also had higher blood leptin levels. But that didn't prompt them to
burn more calories.
Scientific contact: Susan B. Roberts,
Jean Mayer USDA Human
Nutrition Research Center on Aging at Tufts University, Boston,
Mass., phone (617) 556-3237, fax (617) 556-3344,