Levels of adiponectin, another hormone involved in metabolic processes, were increased in the mice. Lower levels of adiponectin are associated with obesity.
The scientists were able to rule out changes to the hypothalamus, a part of the brain involved in "energy homeostasis" or balance, and they also ruled out alterations in glucose metabolism as reasons for the increased leanness.
Adrenaline levels, however, were found to be higher in the lean mice. "This is the interesting part," He said. "Why did adrenaline levels increase? There are several unanswered questions."
Once questions like those are answered, the findings may pave the way for more effective treatments to combat obesity and its myriad complications.
Of course, there are well-known ways of losing weight: lifestyle changes. These are "long-term proven strategies but people won't do them," Weiss said. "People are not comfortable following long-term diet and exercise plans." And with obesity rates continuing to soar in the United States, "we need medical approaches," he said.
There's more on obesity at the U.S. Centers for Disease Control and Prevention.
SOURCES: Stuart Weiss, M.D., clinical assistant professor, medicine, New York University School of Medicine, New York City; Weimin He, Ph.D., assistant professor, Institute of Biosciences and Technology, Texas A&M Health Science Center, Houston; Feb. 22, 2009, Nature
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