A hormone that affects hunger acts in surprising and different ways in lean and fat men -- a finding that may offer new ways to treat obesity, U.S. researchers reported Monday.
Tests on 10 men showed the thin men had an overnight spike in the hormone, called ghrelin, while the five fat men did not.
Ghrelin is the latest in a line of hormones discovered in recent years that act on appetite and eating behaviors. Another hormone, called leptin, makes fat rats lose weight when injected but in humans has little effect -- showing that these compounds interact in complex ways in people.
System gone awry?
Dr. Julio Licinio, a professor of psychiatry and medicine at the University of California Los Angeles and colleagues tested 10 volunteers, keeping them overnight in their lab and carefully feeding them a controlled diet. They took regular blood samples and tested ghrelin levels, among other things.
They were surprised to discover a giant burst of ghrelin in the lean men’s blood between midnight and dawn. It was a bigger spike even than that seen just before a meal, they wrote in this week’s issue of the Proceedings of the National Academy of Sciences.
In the fat men, ghrelin levels stayed level all night long.
“The most powerful ghrelin surge was missing in the obese men, suggesting that their regulatory system has gone awry or can no longer listen to its own cues,” Licinio said in a statement.
“At first glance, our findings appear contradictory. You’d expect the blood levels of the heavier men to contain more hunger hormone. Something must be overriding obese persons’ ghrelin,” he added.
The finding also shows that the hormone peaks in people of normal weight while they are asleep -- when they are unlikely to eat. None of the lean men woke up hungry, they said.
“This defies the stereotype of overweight people waking up in the middle of the night to raid the refrigerator,” Licinio said. “The men in our study slept through the night, and both groups ate meals designed to maintain their current weight.”
They also noted that the obese men in general responded less to ghrelin cues -- when they ate, ghrelin levels did not fall, as they do in thinner people.
Other studies have linked ghrelin to diabetes and high blood pressure, and the researchers said their findings may help shed light on this.
Obesity may be caused by a complex disruption of hormones that all act on one another, said the researchers. They included a team at Louisiana State University’s Pennington Biomedical Research Center, which does extensive work on obesity.