The study released on Tuesday 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.