A new approach to counteracting obesity may be on its way, according to a study published in the October 27 issue of the Journal of the American Medical Association.

Researchers have discovered that treatment with a hormone called leptin increases the rate of average weight loss, and that people taking the highest doses of leptin saw greater reductions in body fat. The scientists stressed, however, that while the results are promising, more research is warranted.

The study, led by Dr. Steven Heymsfield, director of the human body composition and weight control unit at Saint Luke's-Roosevelt Hospital in New York, included 53 lean and 70 obese people who were randomly selected to self-administer injections of either leptin or placebo for four weeks. In the second part of the study, 47 of the obese patients continued the injections for an additional 20 weeks.

The average weight loss after four weeks for both lean and obese participants was the same, regardless of the dose of leptin. Those taking 0.1 milligrams of leptin lost approximately 4.2 pounds, compared with those taking placebo, who lost only 0.9 pounds, on average.

The researchers also found that after 24 weeks, the participants lost more weight as the doses of leptin increased. The following results include the leptin dose and number of pounds lost after the additional 20 weeks of treatment: .01 milligrams leptin, 1.5 pounds; .03 milligrams leptin, 3.1 pounds; .10 milligrams leptin, 5.3 pounds; and .30 milligrams leptin, 15.6 pounds.

Those taking placebo lost an average of 2.9 pounds after the additional 20 weeks.

The lean participants, average 158.6 pounds, were put on a diet during the study that was designed to maintain their body weight as measured when the study began. The obese participants, average 197.8 pounds, were put on a diet designed to reduce their daily calorie intake by 500 less than needed to maintain their body weight.

Results of the study were being presented at the American Medical Association's 18th Annual Science Reporters Conference at the University of California at Los Angeles.

There is a ``relationship with weight and fat loss in conjunction with leptin,'' Heymsfield said. ``Based on this study, administration of leptin injections appears to induce weight loss in some obese subjects.''

Leptin is a hormone associated with the regulation of weight. A previous study suggests that leptin acts as a signal, alerting the hypothalamus -- a part of the brain that coordinates basic body functions, including eating -- of how much fat is in the body.

Differences in the production rate of leptin, resistance to leptin or a combination of those factors may influence eating behaviors and energy used, which may cause obesity or other conditions associated with nutrition, including diabetes.

Heymsfield said that it will be ``at least several years'' before a potentially usefully therapeutic agent based on leptin will be developed. Additionally, he emphasized that leptin is not a ``magic bullet'' -- an agent that will significantly reduce weight levels without the aid of exercise and a modified diet.

He added, however, that ``it is not out of the realm of possibility'' that, in the future, a combination therapy will be developed that will effectively ``shut off the desire for appetite. If biological signals are what control food intake,'' he said, ``I'm confident that some day we will be able to switch that off biochemically.''