Relationship between ghrelin and energy expenditure in healthy young women.

Ghrelin is a novel peptide that has been isolated from human and rat stomach tissues. Despite its known stimulatory effects on appetite and eating behavior, little information is available regarding its relationship with energy expenditure in normal-weight humans. To address this issue, we examined the relationship between serum ghrelin and resting metabolic rate (RMR), the thermic effect of food (TEF), fasting and postprandial respiratory quotient, physical activity level, peak aerobic capacity (VO(2 peak)), energy intake, and psychological measures of feeding behavior. We recruited 65 young healthy women and determined RMR and TEF by indirect calorimetry after a 12-h fast. Physical activity was determined by a leisure time physical activity questionnaire; VO(2 peak) was determined by bicycle ergometer test to exhaustion; energy intake was determined by a 24-h dietary recall; and food behavior was determined by a three-factor eating questionnaire. Our cohort showed a broad range of body mass index (range, 16.8-28.3 kg/m2), RMR (range, 820-1550 kcal/d), TEF (range, 74.4-136.5 kcal/d), and percent body fat (range, 14.0-37.7%). We noted significant inverse correlations between ghrelin and RMR (r = -0.350, P = 0.004) and TEF (r = -0.396, P = 0.001). These inverse correlations persisted after statistical control for both fat-free mass and fat mass (ghrelin vs. RMR partial, r = -0.284, P = 0.024; and ghrelin vs. TEF partial, r = -0.329, P = 0.01) and insulin levels (ghrelin vs. RMR partial, r = -0.255, P = 0.046; and ghrelin vs. TEF partial, r = -0.287, P = 0.024) using partial correlation analysis. We also observed a significant inverse correlation between ghrelin and daily caloric intake (r = -0.266, P = 0.032), but ghrelin levels were not significantly correlated with fasting (r = -0.002), postprandial respiratory quotient (r = -0.016), leisure time physical activity (r = 0.104), VO(2 peak) (r = 0.138), dietary disinhibition (r = -0.071), dietary restraint (r = 0.051), or feeling of general hunger (r = -0.028). These results suggest that higher levels of ghrelin are associated with low levels of resting and postprandial thermogenesis, which is independent of individual differences in fat-free mass and fat mass. Although speculative, serum ghrelin may play a role in the regulation of energy homeostasis by acting as a hormonal marker of increased energy efficiency.

Metabolic and behavioral characteristics of metabolically obese but normal-weight women.

A unique subset of individuals termed metabolically obese but normal weight (MONW) has been identified. These young women are potentially at increased risk for development of the metabolic syndrome despite their young age and normal body mass index. We seek to determine metabolic and behavioral factors that could potentially distinguish MONW women from young women with a normal metabolic profile.Ninety-six women were classified as MONW (n = 12) or non-MONW (n = 84) based on a cut point of insulin sensitivity (as estimated by the homeostasis model assessment). Potentially distinguishing phenotypes between groups measured included serum lipids, ghrelin, leptin, adiponectin, body composition and body fat distribution, resting and physical activity energy expenditure, peak oxygen uptake, dietary intake, dietary behavior, and family history and lifestyle variables. Despite a similar body mass index between groups, MONW women showed higher percent body fat, lower fat-free mass, lower physical activity energy expenditure, and lower peak oxygen uptake than non-MONW women. Plasma cholesterol level was higher in MONW women, whereas no differences were noted for other blood lipids, ghrelin, leptin, adiponectin, and resting energy expenditure. MONW women had lower dietary restraint scores than non-MONW women, but no differences were noted in disinhibition, hunger, and dietary intake. Stepwise regression analysis performed on all subjects showed that 33.5% of the unique variance of the homeostasis model assessment was explained with the variables of percentage of body fat (17.1%), level of dietary restraint (10.4%), and age (6%). Both metabolic and dietary behavioral variables contribute to the deleterious metabolic profile of MONW women. They display lower insulin sensitivity due potentially to a cluster of sedentary behavior patterns that contribute to their higher adiposity. Furthermore, cognitive attitudes toward food (i.e. dietary restraint) and concomitant lifestyle behaviors may play a role in regulating insulin sensitivity in MONW women.