What happened to leptin?

By Laura Lane

(WebMD) -- It's been four years since scientists first announced that they had found a hormone that could be the answer to the cries of the obese. Leptin, as scientists dubbed the hormone, helped obese mice to lose weight and possibly could do the same in people.

As clinical trials progress, though, leptin is not looking to be quite as effective as first thought, said Dr. Daniel Porte Jr. of the University of Washington School of Medicine in Seattle, who has been studying obesity for more than 20 years.

The hormone has been effective in the 5 percent of obese people who lack the ability to make leptin, he said. Otherwise, for the vast majority of the obese, the hormone has been largely ineffective in reducing weight. In fact, because fat cells produce leptin, most obese people have high levels of the hormone, which encourages the brain to make alpha-MSH, which goes on to regulate body weight somehow.

And while Porte said that the new finding is a "positive step," scientists need to learn more about the complex inner workings of the body's weight-regulation system before an effective obesity medication can be developed.