Individuals with constitutional thinness are characterized by an atypical resting energy metabolism and body composition. The aim of the present study was to compare patterns of energetic changes from a fasted resting state to i) postprandial resting, ii) fasted exercise, and (iii) postprandial exercise between females with constitutional thinness and normal-weight, considering body weight and composition characteristics. Subjects/MethodsBody composition (X-ray absorptiometry) and maximal aerobic capacities were assessed in 17 female adults with constitutional thinness and 17 normal-weight controls. Their energy expenditure and substrate oxidation were assessed by indirect calorimetry on four occasions: i) in a fasted resting state, ii) two hours after a calibrated meal in a resting state, iii) after a 30-min cycling exercise performed postprandially, and iv) after a 20-min walking exercise in a fasted state. ResultsFemales with constitutional thinness had significantly lower body weight (p < 0.001), absolute fat-free mass (p < 0.001) and percentage of fat mass (p = 0.04). Energy expenditure was lower for all the energetic stimuli considered (from p = 0.02 to p < 0.001) in participants with constitutional thinness compared to normal-weight controls, and differences disappeared after adjustment for body weight or composition. ConclusionsThe present results do not indicate any impaired energetic responses to any energetic stimuli in females with constitutional thinness. Results challenge the hypothesis of a spender energy profile in individuals with constitutional thinness, and highlight the necessity to gain insight into the role of body composition in energetic regulation in this population.