The researchers at the University of Texas Southwestern Medical Center found mice with increased levels of the chemical orexin don't gain weight when fed a high-fat diet. The chemical works by increasing the body's sensitivity to the so-called "weight-loss hormone" leptin, the researchers said.
Professor Masashi Yanagisawa, senior author of the study, said finding a way to boost the orexin system might prove useful as a therapy against obesity.
"Obese people are not deficient in leptin," Yanagisawa said. "They have tons of leptin floating around. The problem is that their brain isn't very sensitive to it."
The researchers said they increased the levels of orexin in mice by either genetic engineering or by administering the hormone into the brain. When the mice were fed a healthy diet, the increased levels of orexin made little difference in their weights, the scientists said. But when the mice were fed a high-fat diet, the high-orexin mice remained lean while the normal animals became obese.
The research appears in the January issue of the journal Cell Metabolism.