Contrary to popular belief, overeating may be the fault of the brain, not the stomach.

Leptin, a human protein hormone that regulates food intake, has been linked with significant fat loss in laboratory rats. But scientists say it would be premature to assume that more leptin in humans would lead to less bulge at the waist line.

Laboratory rats that were genetically altered to produce large amounts of leptin lost twice as much body fat as normal rats when fed the same diet, according to a study published yesterday by researchers at the University of Texas Southwestern Medical Center at Dallas. The study showed that leptin both reduced the rats’ appetite and altered the metabolism of fat.

Studies of humans have shown, however, that high levels of leptin are found in heavier individuals. Their overindulgence may be the result of a neurological disorder.

Laurence Tecott, a UCSF neuroscientist who is examining the neuroregulation of appetite, says a neurological resistance to leptin in obese humans may explain why they overeat.

“One possibility is that the brain is less sensitive to the leptin signal, so that the signals telling your brain to terminate a meal may be less effective,” he says.

“The question becomes, can leptin resistance be safely overcome by administering very high doses of the protein.”

Maybe. The rats who lost the fat were genetically altered to produce 20 times as much leptin as normal rodents.

1st appeared 4/30/97