Two out of three US adults are overweight or obese. This is alarming since overweight and obesity contribute to a multitude of health problems, including heart disease , diabetes , stroke , arthritis , and cancer. A variety of weight-loss medications, supplements, and programs exist, but their rate of success is generally very low over the long-term. In fact, to date, surgery (i.e., gastric bypass) is the only truly effective treatment for morbid obesity.

Are less expensive, less invasive treatments on the horizon? Researchers have been studying a variety of hormones that control hunger and regulate body weight. Among these is leptin, which has been shown to curb the appetites of normal-weight individuals but not obese people (obese people show a resistance to leptin).

Recently, researchers have been looking into a hormone produced in the gut called peptide YY3-36 (PYY). Like leptin, PYY acts as a messenger to signal to your brain that you are full. Studies have shown that infusions of PYY reduce food intake in normal-weight individuals and decrease weight gain in rodents over the long-term. Furthermore, PYY may suppress the production of the “hunger hormone” ghrelin, which rises before a meal (signaling hunger) and falls after a meal (signaling fullness).

But can PYY help obese people lose weight? In a new study in the September 4, 2003 issue of the New England Journal of Medicine , researchers compared the effects of PYY infusion in obese and lean people. They found that compared to saline (salt water), PYY significantly decreased food intake at an all-you-can-eat buffet lunch in both lean and obese people. In addition, PYY dramatically decreased calorie consumption over a 24-hour period in all participants.

About the Study

The participants in this study were healthy lean and otherwise healthy obese people who had had a stable body weight for at least three months. The body mass index (BMI is a measure of body fat based on height and weight) of the lean group was between 17 and 23, and the BMI of the obese group was between 27 and 40. There were 12 participants in each group (six men and six women).

Each participant came in on two days, one week apart. They consumed a standardized diet during the 48 hours before each study day and refrained from alcohol and strenuous exercise for 24 hours before and after each study day.

During the study days, participants received a 90-minute infusion of either saline or PYY. To measure levels of PYY and other appetite controlling hormones (ghrelin, leptin, and insulin), blood was collected 30 minutes before the infusion began and every 30 minutes until it ended.

Two hours after the infusion ended, the participants were offered an all-you-can-eat buffet lunch. The researchers measured the amounts of food and water each participant consumed. The participants rated their levels of hunger, nausea, and meal palatability and kept track of their food intake for 24 hours.

On the second study day (one week later), the same protocol was followed, with each participant receiving an infusion of saline or PYY, whichever they hadn’t yet received. Neither the participants nor the researchers were aware of whether the infusions contained saline or PYY.

The Findings

Compared with saline, PYY significantly reduced calorie intake during the buffet lunch in both lean and obese participants, by 31% and 30%, respectively. Furthermore, over the course of 24 hours, PYY substantially reduced calorie intake in all participants (by 24% in the lean group and 17% in the obese group). The PYY infusion reduced reports of hunger in both obese and lean groups and did not affect reports of nausea or palatability of meals.

When the subjects were receiving saline, fasting PYY levels were significantly lower in the obese than in the lean group. While the PYY levels increased in both groups after the meal, the obese group’s PYY response was significantly smaller than the lean group’s, even though the obese group consumed more calories.

Regarding the other appetite-control hormones, PYY significantly reduced the fasting ghrelin levels in both groups and reduced post-meal ghrelin levels in the lean group. Leptin and insulin levels were not affected by the PYY infusion.

How Does This Affect You?

The results from this study support previous findings that PYY may be a beneficial weight-loss therapy. This study was the first to show that obese and lean people respond similarly to PYY. Furthermore, these findings suggest that obese people have low levels of circulating PYY, which supports the theory that a PYY deficiency may be involved in obesity.

But don’t expect PYY to become available anytime soon. This study only tested a single infusion of PYY, which cannot determine its long-term effects. And PYY is only one piece of the puzzle. Since the hormones involved in appetite control are highly interrelated, it is unlikely that PYY—or any other single drug—will be the miracle cure for obesity.

These findings do suggest, however, that increasing PYY levels in obese people could potentially control their appetite and aid in weight loss. Future research is needed to determine the safety and efficacy of PYY for treating obesity over the long run.