Hormone treatment reduces appetite: study

Sep 05 (HeartCenterOnline) - British researchers find that an infusion of a gut-derived hormone reduces appetite in both obese and lean individuals. The study is published in the September 4 issue of the New England Journal of Medicine.

Obesity is a condition in which people are more than 20 percent over their ideal weight and/or have a body mass index greater than 30. Currently, more than one-third of Americans are obese.

Generally, obesity develops when the amount of energy units (calories) consumed through food is greater than the energy spent through metabolism and physical activity. Excess calories are stored in the body as fat; if too much body fat builds up, weight gain is inevitable. People also tend to gain more weight if they are older and/or have a low metabolic rate. Other factors (e.g., genetic, socioeconomic, psychological and medical) are also involved, but the relationship among these factors and the extent to which each contributes to obesity is less understood.

As a major risk factor, obesity is the second leading cause of preventable death, surpassed only by smoking. There are two basic ways in which obesity increases the risk of heart disease. First, it can indirectly contribute to heart disease by causing changes in the body that increase the risk of heart disease, such as raising levels of cholesterol and triglycerides, increasing blood pressure and the risk of type 2 diabetes. The second way in which obesity increases the risk of heart disease is by causing unhealthy physical changes in the heart itself (e.g., enlargement and thickening -hypertrophy- of the left ventricle hypertrophy).

It is believed that heredity (genetics) plays a strong and perhaps dominant role in the development of obesity. One area of research in this area has been the study of leptin, a hormone that regulates appetite. If an individual has consumed too much food and is gaining weight, leptin levels increase to decrease appetite and increase energy use. On the other hand, if an individual is losing weight, then leptin levels should decrease to stimulate the appetite and reduce energy use. The point where a signal is sent to the brain to increase or decrease leptin levels is called the set point, a weight that is relatively stable in a given individual, but which may vary considerably among the general population. Not producing enough leptin, therefore, would increase the risk of being overweight or obese.

Studies have demonstrated that obese patients have a higher set point at which leptin levels are released. In other words, obese individuals have a biological resistance to the action of leptin.

In the current study, Rachel L. Batterham and colleagues from the Imperial College Faculty of Medicine (London) focused on a specific hormone found in the gut, called PYY. It is similar to leptin, in that it impacts on brain activity involved in regulating appetite. Since obese persons demonstrate a resistance to leptin, the researchers sought to determine whether or not there was resistance to PYY.

Twenty-four subjects - 12 obese and 12 lean - were selected to receive an infusion of either PYY or an inactive placebo (in this study, saltwater). The infusions were administered at 8:30 a.m. Two hours later, all subjects were given a buffet lunch. Obese subjects given PYY consumed 30 percent fewer calories during the buffet than did their placebo counterparts. PYY given to lean subjects led to a 31 percent decrease, compared to placebo. Over a 24-hour period, PYY obese subjects ate a total of 1,180 calories; placebo obese subjects, 2,456. PYY lean subjects ate a total of 1,533 calories, with placebo lean subjects consuming 2,312.

The results showed that obese subjects did not demonstrate a resistance to the appetite-suppressing effects of PYY. Moreover, blood tests conducted during the study found that the obese subjects had intrinsically low levels of PYY. The researchers infer that the onset and course of obesity may be due, at least in part, to a PYY deficiency.

For more information on this topic, visit HeartCenterOnline's Weight & Obesity Center.