As rates of obesity continue to rise, scientists continue to study the potential causes of and treatments for the condition. Scientists in the United Kingdom recently found that a substance called peptide YY_3-36 (PYY), which is produced in the gastrointestinal tract, may play a pivotal role in the battle of the bulge. Their findings are published in the New England Journal of Medicine.

Studying PYY's effects on food intake

PYY, secreted by the gastrointestinal tract, is involved in appetite and regulation of food intake. The authors of this study had shown in previous research that injections of PYY reduced food intake in normal-weight subjects. This time, using the same experimental design, they included both obese and normal-weight subjects to see if results would differ between the two.

The researchers studied 12 obese and 12 normal-weight volunteers (six men and six women in each group; average age: 29 in the obese group and 27 in the normal-weight group). They gave the subjects injections of either PYY or saline (a weak salt solution) 2 hours prior to offering them a buffet lunch. Neither the researchers nor the subjects knew which subjects were receiving PYY and which were receiving saline. After one week, the two groups were switched, so that by the end of the study, all subjects had received PYY once and saline once.

The researchers calculated how many calories the subjects consumed at the buffet lunch and required them to record their food intake for an entire 24-hour period. They also assessed the subjects' level of hunger after receiving their injections.

PYY inhibits appetite and food intake

When obese and normal-weight subjects received PYY, both groups consumed fewer calories during the buffet lunch. Caloric intake was reduced by 30% in the obese subjects and by 31% in the normal-weight subjects when they received PYY. As a result of eating less at the buffet lunch, subjects also had a cumulative decrease in their 24-hour food intake.

Uncovering PYY's association to obesity

The researchers also measured blood levels of PYY in all subjects before and after they ate. PYY levels were significantly lower in obese subjects compared with normal-weight subjects. This raises the question of whether low levels of PYY cause obesity, or obesity causes low levels of PYY.

While we don't yet know the order of things, these findings indicate that PYY may play a pivotal role in regulating food intake and that administering it to obese people may help them consume fewer calories. However, it's important to note that this was a small study of only 24 subjects, and that numerous additional studies involving more subjects are necessary before a treatment based on PYY could reach the market. There have been other substances (e.g. leptin) that have raised hopes this far, only to have failed in clinical trials.

In the meantime...

As scientists continue to search for potential treatments for obesity, experts continue to recommend the "tried and true" advice: Either eat fewer calories or burn more calories through exercise - or, better yet, do a combination of both.