Despite the researchers' forecasts, the discovery of ghrelin, the appetite-enhancing hormone, was not the last breakthrough in the field of weight regulation. They've discovered a new hormone, called obestatin, whose effect is opposite to ghrelin.

Researchers at the Stanford University School of Medicine uncovered obestatin by using the principles of evolution to pick clues from data held in the Human Genome Project, as well as the genome sequencing projects for many other organisms, among them, yeast, fruit flies and mice.

"Darwin led us to this new hormone", said senior author Aaron Hsueh, PhD, an endocrinologist and professor of obstetrics and gynecology. Jian V. Zhang, PhD, a postdoctoral scholar in Hsueh's laboratory, is the lead author.

"There are several known pathways that regulate body weight: ghrelin, leptin and melanocortin," explained Greg Barsh, MD, PhD, a Stanford professor of genetics who studies melanocortin and was not involved in the obestatin project. "This work is notable because it represents a completely new pathway."

The identification of obestatin occurred as part of the researchers' study of a specific category of hormones-relatively small protein molecules called peptide hormones. These are of particular interest to drug developers because they bind to a type of receptor molecule known as a G-protein-coupled receptor, or GPCR.

"These receptors represent targets for almost 50 percent of the drugs in the market," said Hsueh.

They found that injecting it into rats' abdomens and brains decreased food intake and suppressed weight gain. Rats given obestatin injections ate about half as much as those given no obestatin. Obestatin treatment also slowed the movement of digested food from the stomach into the intestines.