WEDNESDAY, Sept. 3, 2003 (HealthDayNews) -- Injections of an appetite protein normally secreted in the intestine significantly trimmed the urge to eat in both thin and obese people, a new study finds.
The discovery could lead one day to treatments for obesity, the researchers say, although other experts contend such a claim is premature.
The protein is called peptide YY (PYY), and it reduces food intake by sending signals of satiety to the brain. Previous research had shown that normal weight people don't eat as much when given doses of PYY before a meal. The latest study finds the effect is equally potent in the obese, cutting short-term food intake by about 30 percent in both groups.
"We didn't know whether PYY would work in the obese," says study leader Dr. Stephen Bloom, a diabetes expert at London's Imperial College. "But when we administered PYY it was fully effective. That is the first step for trying to establish it as a therapy for obesity."
The protein didn't cause any obvious side effects -- not surprising, Bloom adds, since the body releases a wash of it after every meal.
A report on the finding appears in the Sept. 4 issue of the New England Journal of Medicine.
L. Arthur Campfield, an appetite expert at Colorado State University, says the latest work is "too preliminary for people to get excited about, but it is very promising." The 30 percent decrease in food intake is "a good reduction and if it could be sustained it should lead to a negative energy balance and weight loss."
But a few aspects of the study are troublesome, Campfield says. The researchers used a single dose of PYY given once, and everyone in the study appeared to respond to the peptide. That's unusual, he says.
In addition, the subjects reported modest reductions in hunger after receiving PYY yet experienced substantial declines in food intake. That suggests some other factor, such as nausea or an unpleasant change in the appeal of food, was also at play.
Bloom's group says the volunteers didn't experience nausea or altered appreciation of food after receiving PYY.
Obesity accounts for 280,000 deaths a year in the United States, from heart disease, cancer and other conditions affected by weight. While dieting and exercise can help people slim down, scientists -- and those plagued by weight problems -- have long sought a drug therapy.
Bloom and his colleagues studied the effects of PYY in 12 fit and 12 obese men and women. Upon entering the study, the obese subjects had roughly 40 percent lower levels of the peptide than their slim peers.
Bloom calls that difference "very important" since it gives the obese a greater tendency to eat. "They don't have the same level of satiety hormone that thin people have."
Why PYY was so low in the obese study subjects, however, isn't clear: It could reflect prolonged overeating or be the cause of overeating.
The researchers first gave infusions of PYY or a saline solution to each group, and two hours later offered them lunch at a no-holds-barred buffet with so much chicken curry and other foods that "all appetites could be satisfied." Afterward, a dietitian tallied the amounts of food and water eaten and calculated the calorie content of the meal.
Then they repeated the experiment so all of the 24 volunteers had received the peptide.
When under the influence of PYY, the obese subjects ate 30 percent fewer calories than they did after receiving the placebo -- virtually identical to the 31 percent drop in caloric intake seen in the thin group.
The peptide reduced appetite for up to 12 hours, but not beyond, in both obese and lean men and women.
The reduced food intake from PYY injections did not appear to be the result of nausea or illness from the protein, the researchers say.
But whether it can promote weight loss is another matter entirely, says Dr. David Cummings, an appetite expert at the University of Washington in Seattle.
"Does it serve to terminate one meal, or is it a regulator of body weight over the long haul?" says Cummings, who studies another appetite hormone called ghrelin. Tinkering with PYY may encourage people to adapt to their lack of hunger by eating smaller meals more frequently -- and thus keep pounds on.
That kind of compensation -- demonstrated with other appetite hormones -- has been strongly influenced by evolution, he says.
"Body weight, particularly the loss of body weight, is robustly defended against by different pathways. Manipulation of any one may be compensated for by increases in the others," Cummings says. "Over the eons the systems that evolved to protect against weight loss were constantly being refined by famines, which killed off anyone who wasn't good at storing fat."
Ultimately, he says, drug treatment for obesity likely will be a cocktail of medicines that target several different pathways in the appetite regulation system.
More information
To learn more about how to set up a healthful diet, try the American Dietetic Association or the National Heart, Lung, and Blood Institute.
