In a newly published study, both normal-weight and overweight people ate roughly a third less after getting infusions of the hormone PYY.
The findings offer the hope that PYY, which is produced in the gut, may one day help fulfill the failed promise of the widely studied hormone leptin, which is made in fat cells. Drugmaker Amgen spent millions to develop leptin as a weight-control drug. But though studies in mice were promising, the hormone proved to have little effect on appetite and weight control in humans.
"PYY signals the brain that a person is full," researcher Stephen R. Bloom, MD, tells WebMD. "We have shown that overweight people have PYY deficiencies and that their response to PYY infusions is the same as in thin people. They eat less because they are not as hungry."
How PYY Affects Weight Control
In the study, published Sept. 4 in TheNew England Journal of Medicine, Bloom and colleagues examined the effect of PYY on appetite and calories eaten in 12 obese and 12 thin people. All participants were given infusions of PYY designed to mimic the natural rise in the hormone produced by eating a meal. Two hours later, they were served an all-you-can-eat lunch, and both groups ate roughly 30% fewer calories.
In addition, all the study participants ate less over the following 24 hours. They did not eat more later to make up for the less food eaten just after the PYY infusions.
"We were able to fool the brain into thinking that the stomach was full by giving the natural amount of PYY that a normal person would produce after a meal," Bloom says. "Obese people are short on PYY, so it ought to be useful to give it back again."
The next step, Bloom says, is to study whether PYY actually holds promise as a weight-control treatment -- whether it can help overweight people lose pounds.
More Hormone Answers?
Another gut hormone that has been studied for its weight-control potential, called ghrelin, has also been found to play a major role in hunger. It appears that ghrelin signals the brain to stimulate appetite just as PYY signals the brain when the stomach is full. Columbia University professor Rudolph Leibel, MD, who is also researching how hormones affect weight control, says it is now clear that the brain interacts with gut hormones such as PYY and ghrelin and fat hormones such as leptin to control appetite and body weight.
Leibel tells WebMD he is optimistic that the hormone research will result in better treatments for weight control, but he doesn't believe that PYY or any other single hormone will end up being the "magic bullet" for weight loss. He is head of the division of molecular genetics at Columbia's College of Physicians and Surgeons.
"The understanding of these pathways is going to lead to the development of entirely new types of treatment for obesity," he says. "Rather than one of these molecules being the answer, it is more likely that a combination of several of them or their derivatives or agents that work on their receptors will hold the answer. My guess is that within the next five to 10 years there will be a series of agents that target food intake and body weight in a way that is radically different from the drugs that are available today."