Negative Relationship Between Fasting Plasma Ghrelin Concentrations and Ad Libitum Food Intake

Ghrelin is a novel GH secretagogue with orexigenic effects. We hypothesized that high fasting plasma ghrelin concentrations (FxGhr) might predict high ad libitum food intake. FxGhr were measured in 30 normoglycemic subjects: 15 Pima Indians (8 male/7 female; age, 32 +/- 7 yr; body weight, 87 +/- 21 kg; mean +/-sd) and 15 Caucasians (12 male/3 female, 36 +/- 8 yr, 94 +/- 26 kg) in energy balance for 3 d before testing. Subjects then self-selected their food ad libitum for the following 3 d. Mean daily energy intake (DEI) was calculated from the weight of foods consumed and expressed as a percent of weight maintenance energy needs. FxGhr were twice as high in Caucasians as in Pima Indians (103 +/- 53 vs. 52 +/- 18 fmol/ml, P < 0.001) and remained higher after adjustment for age, gender, and body weight (P < 0.0001). Neither DEI, nor percent of weight maintenance energy needs, nor percent of calories from fat differed between the races. In both groups, FxGhr were negatively correlated with DEI (r = -0.61, P = 0.01; r = -0.54, P = 0.04, respectively). These negative relationships were not explained by interindividual differences in age, gender, or body weight. This unexpected finding that low FxGhr predict ad libitum food intake suggests that the role of endogenous ghrelin in the regulation of energy homeostasis remains uncertain.