By Merritt McKinney
NEW YORK (Reuters Health) - A hormone that triggers hunger may be released on a different schedule in obese people than in thin people, researchers report.
In a small study, levels of the "hunger hormone" ghrelin peaked when lean men were asleep. But obese men did not experience a surge of the hormone during the night.
"That may help explain why obese people are eating more," lead author Dr. Julio Licinio at the University of California at Los Angeles told Reuters Health in an interview. Licinio explained that ghrelin is the only circulating hormone that encourages people to eat. When levels of the hormone rise, people get hungry.
The California researcher noted that for normal-weight men in the study, "the highest amounts of ghrelin are in the middle of the night when they are sleeping "when they cannot eat."
In contrast, in the obese, "at night the levels don't go up," Licinio. This means that ghrelin levels are at their highest during the day, when people can satisfy their hunger by eating, he said.
Licinio said he would like to see what happens to the pattern of ghrelin levels when people lose or gain weight.
"I'd like to see if these patterns are different," Licinio said. He noted that even after people lose weight, it is not easy to keep the extra pounds from coming back. Licinio said it will be interesting to see if people who were obese begin experiencing nighttime surges in ghrelin as other lean people do.
Ghrelin is one of several hormones being studied by obesity researchers. Ghrelin is known as the hunger hormone because people given the hormone in previous experiments became so hungry that they ate up to one third more food than usual.
Another hormone called adiponectin, which is secreted by fat tissue, seems to affect how well the body responds to the sugar-processing hormone insulin.
Leptin, another hormone released by fat cells, tells the brain to curb appetite. However, most obese people have elevated levels of the hormone, suggesting that they may be resistant to its appetite-suppressing effect.
The release of hormones varies throughout the day, so Licinio and his colleagues set out to look for obesity-related differences in how ghrelin, adiponectin and leptin circulate.
The study included five obese men and five lean men whose hormone levels were measured every 7 minutes over a 24-hour-period.
Levels of adiponectin and leptin varied between obese and lean men, Licinio explained. But he noted that the general patterns of how these hormones were released were similar in both groups of men.
That was not the case with ghrelin, Licinio and his colleagues report in the advance online edition of the journal Proceedings of the National Academy of Sciences.
As mentioned, obese participants did not experience a surge of the hunger hormone while sleeping as lean men did.
While the findings do not mean that differences in ghrelin patterns make people gain weight, Licinio said that they could play some role in obesity.
Licinio cautioned that the patterns need to be studied in larger groups of men, as well as in women. Licinio and his colleagues have already started a similar study in women.
SOURCE: Proceedings of the National Academy of Sciences Early Edition, June 28, 2004.