Obesity may be hard-wired into the brain from birth, according to a new animal study released Tuesday that appears to bolster the notion that some people are more prone to pile on the pounds than others.

The study showed that obese rats had faulty brain wiring that impaired their response to the hunger-suppressing hormone leptin.

In obesity-prone rats, "it seems that appetite and obesity are built into the brain," said Sebastien Bouret, an assistant professor of neuroscience at the University of Southern California, Los Angeles.

"The neurodevelopmental differences in these animals can be seen as early as the first week," he said.

"The results show that obesity can be wired into the brain from early life. The three-million-dollar question now is how to get around the problem."

Leptin plays a central role in fat metabolism. Produced by fat tissue, it acts as a signal to the brain about the body's energy status.

Its role in weight regulation is still unclear, but what scientists do know is that the brain calibrates the need for food intake based in part on leptin levels.

Previous research had shown that the brains of obesity-prone rats were insensitive to these leptin signals, so the researchers looked for brain abnormalities that could explain this.

They found defects in the brain circuits that relay leptin signals throughout the hypothalamus -- the brain's central switchboard for regulating conditions in the body.

While the rats' condition might be improved by exercising and eating right, the findings suggest that the propensity to gain weight can't be reversed, Bouret said.

If the findings are replicated in humans, then those individuals who are genetically predisposed to obesity because of the way their brains are configured would have to be very careful about "diet and energy balance," said Richard Simerly, another researcher who worked on the study.

The findings also fly in the face of the one-size-fits-all approach that characterizes much of the discussion about weight management and weight loss in the media, said Simerly, who is director of the neuroscience program at the Saban Research Institute at the University of Southern California.

"The message in the media that weight regulation is all a matter of nutrition or lifestyle choices does a disservice to people whose biology predisposes them to obesity," he said.

The study appears in the February issue of Cell Metabolism.

CHICAGO, Feb 5, 2008 (AFP)


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