Vaccine against fat!: "Scientists have vaccinated rats against a weight-gain hormone, allowing them to eat freely without getting fat, in a development that raises hopes for treatments for overweight and obese humans. The vaccine operates against ghrelin - a recently discovered hormone among several which appear to regulate metabolism. Ghrelin is thought to be implicated in a problem that frustrates many dieters: the tendency for weight to be regained even after successful dieting. Researchers believe the phenomenon would have conferred an evolutionary advantage among early humans, whose food supply was irregular - ensuring maximum use of available calories during times of famine and programming the body to return quickly to its highest weight."