By Mike Fillon
NEW ORLEANS, LA -- June 21, 2004 -- In people who have had gastric bypass surgery, a gastrointestinal hormone called peptide YY (PYY) may play an important role in promoting weight loss and maintenance by inducing a greater sense of fullness soon after a meal, leading to decrease in meal size.
These findings were reported here June 18th during a clinical oral session at the 86th Annual Meeting of The Endocrine Society.
The hormone ghrelin acutely increases appetite by inducing hunger and signaling the need to eat, while PYY decreases food intake in people by inducing satiety or a sense of fullness and the desire to stop eating. It is well known that when people try to lose weight by decreasing their caloric intake, they become very hungry. As a result, even if they are able to lose weight, they cannot keep the weight off.
According to researcher Judith Korner, MD, Florence Irving Assistant Professor of Clinical Medicine, Columbia University, New York, Roux-en-Y gastric bypass surgery (RYGBP) is an effective means of producing weight loss and long term maintenance of a lower body weight. Even though patients eat less after this surgery, they usually do not experience increased hunger.
Dr. Korner and colleagues hypothesized that the decrease in food intake and appetite after RYGBP may be due, in part, to changes in the levels of ghrelin and PYY in either fasting and or post-meal states.
To better understand this process, they examined the response of these hormones in lean and obese individuals and in patients who had undergone RYGBP after they drank a liquid test meal. The lean group included 7 women and 3 men with an average body mass index (BMI) of 46 and an average age of 47 years. The group of patients who underwent gastric bypass was composed of 6 women with an average BMI of 32, a pre-operative BMI of 51, and an average age of 45 years.
Average weight loss in the RYGBP group was 37% of initial body weight over a period of 26 months (with a range of 15 to 45 months.) The weight of all participants was stable at the time of the study.
After an overnight fasting period, participants consumed a liquid test meal consisting of 320 calories. Blood samples were drawn before the meal and at 30, 60, 90, 120 and 180 minutes after the meal.
Fasting PPY levels were greater in lean compared with obese and RYGBP subjects. Peak PYY response to the test meal was exaggerated in RYGBP compared with lean and obese subjects. The obese group tended to have a blunted PYY response to food. Fasting ghrelin levels tended to be lowest in the obese group and similar between lean and RYGBP subjects. All groups exhibited a similar decrease -- between 27% and 31% -- in ghrelin levels after consuming the test meal.
According to the researchers, these findings suggest that changes in PYY concentrations, rather than in ghrelin concentrations, may play an important role in promoting weight loss and maintenance after RYGBP by inducing increased satiety and decreased meal size.
Title: "Effects of Gastric Bypass Surgery on Plasma PYY and Ghrelin Responses to a Test Meal." Abstract #OR27-3]