Effects of Weight Loss and Exercise on Fasting Ghrelin

Effects of Weight Loss and Exercise on Fasting Ghrelin

Abstract and Introduction

Abstract

Objective Compensatory metabolic changes that accompany weight loss, for example, increased ghrelin, contribute to weight regain and difficulty in long-term weight loss maintenance; however, the separate effects of long-term caloric restriction and exercise on total circulating ghrelin in humans are unknown.

Design A 12-month randomized controlled trial comparing: i) dietary weight loss with a 10% weight loss goal ('diet'; n = 118); ii) moderate-to-vigorous intensity aerobic exercise for 45 min/day, 5 days/week ('exercise'; n = 117); iii) dietary weight loss and exercise ('diet + exercise'; n = 117); or iv) no-lifestyle-change control (n = 87). Participants: 439 overweight or obese postmenopausal women (50–75 y).

Measurements Fasting total serum ghrelin was measured by radioimmunoassay at baseline and 12 months. Fasting serum leptin, adiponectin and insulin were also measured.

Results Fasting total ghrelin significantly increased in the diet + exercise arm (+7·4%, P = 0·008) but not in either the diet (+6·5%, P = 0·07) or exercise (+1·0%, P = 0·53) arms compared with control. Greater weight loss was associated with increased ghrelin concentrations, regardless of intervention. Neither baseline ghrelin nor body composition modified the intervention effects on changes in total ghrelin. The 12-month change in total ghrelin was inversely associated with changes in leptin, insulin and insulin resistance, and positively associated with change in adiponectin.

Conclusions Greater weight loss, achieved through a reduced calorie diet or exercise, is associated with increased total ghrelin concentrations in overweight or obese postmenopausal women.

Introduction

Ghrelin is an enteric peptide and the only known circulating appetite-stimulating (orexigenic) hormone. It is implicated in short-term control of food intake as well as long-term body weight regulation.

Ghrelin circulates in proportion to body weight (with higher levels of ghrelin seen with lower body weight), and generally responds in a compensatory fashion to weight change (increasing with weight loss, decreasing with weight gain). Ghrelin response to weight loss has been primarily examined in the settings of caloric restriction or surgical intervention, although altered ghrelin concentrations have been observed in response to weight loss through exercise. A recent study suggested that exercise-induced weight loss may increase fasting ghrelin and hunger sensations, but at the same time, it may also balance the orexigenic drive by increasing satiety after a meal and improving the sensitivity of the appetite control system. These observations may account, in part for the mixed findings with respect to the role of ghrelin changes on weight regain.

To our knowledge, no studies have compared the separate and combined effects of long-term (≥12 months) caloric restriction and aerobic exercise on total circulating ghrelin concentrations in humans. This is an important issue; compensatory metabolic changes that accompany weight loss, including increased ghrelin, are hypothesized to contribute to weight regain and difficulty in long-term weight loss maintenance.

The purpose of this study was to examine the independent and combined effects of 12 months of dietary weight loss and/or aerobic exercise on total ghrelin in overweight and obese postmenopausal women, and to assess the degree to which changes are associated with body composition, select adipokines and other metabolic parameters including leptin, adiponectin, glucose, insulin and insulin resistance as assessed by the homeostasis assessment model (HOMA), that may also have roles in regulating energy balance, hunger and satiety.

We hypothesized that ghrelin would significantly increase in the diet and diet + exercise groups compared with controls, and that the magnitude of increase would be proportional to the amount of weight lost.