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"I think it's interesting in that it's another demonstration that leptin may have actions outside of the hypothalamus," says Joel Keith Elmquist PhD, DVM. Elmquist is in the division of endocrinology at Beth Israel-Deaconess Medical Center and is an assistant professor of neurology at Harvard Medical School in Boston.

He adds that a true abnormality in the receptors for leptin is rare in humans, but it's thought that we can have what's called leptin resistance. This phenomenon can be compared with memory loss -- the object is still there, but you don't recognize it. In this case, the body has normal, or even elevated, amounts of leptin, but the cells that need leptin to control food intake or increase energy use no longer recognize it.

"So a lack of response to leptin is thought to very strongly contribute to obesity. Perhaps [that] resistance [occurs] at the level of the taste system as well, [and that] may contribute to ... obesity," Elmquist tells WebMD.

Another Boston-based researcher is less sure.

"Many people [have] ... high leptin levels already, and in human studies of the effect of leptin on weight loss, some people lose weight but many people don't," says Andrew Greenberg, MD, director of the program in obesity and metabolism at the Jean Mayer USDA Human Nutrition Research Center at Tufts University.

Greenberg suggests that although the study's findings are interesting, the exact role of leptin in causing obesity is still unclear. " "Leptin has so many effects; humans who have no leptin, for example, eat lots and lots of food. This may be one piece of the puzzle, but it's probably not a major piece," he tells WebMD.

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