Metabolic and pathophysiological characterization of constitutional thinness

Constitutional thinness (CT) is characterized by a persistently low body weight in the absence of eating disorders or overt disease. Distinguishing CT from anorexia nervosa (AN) is often challenging, and the metabolic and cardiovascular features of CT remain incompletely defined. The present study investigated nutritional, metabolic, and cardiovascular parameters in women with CT and compared them with those of women with AN and normal-weight healthy controls. Data from 7 women with CT were compared with those from 6 women with AN and 6 normal-weight healthy women serving as controls. The resting metabolic rate (RMR) and endothelial function, assessed by flow-mediated dilatation (FMD), were measured. Body weight, body mass index, fat mass and fat-free mass (FFM) were comparable between the CT and AN groups and significantly lower than those of the control group. Absolute and FFM-normalized RMR values were significantly higher in the CT group (median [IQR]: 1263 [247] kcal/24 h and 29.2 [3.1] kcal/FFM-kg/24 h) than in the AN group (1046 [272] kcal/24 h and 25.4 [2.7] kcal/FFM-kg/24 h; P < 0.001 and P < 0.05, respectively), and did not differ from those observed in controls (1317 [221] kcal/24 h and 29.5 [1.2] kcal/FFM-kg/24 h). Flow-mediated dilatation was significantly lower in both the CT (7.2 [2.7] %) and AN (7.6 [6.2] %) groups compared with controls group (14.0 [9.0]%; P < 0.05). These findings indicate that RMR differs between CT and AN, with women with CT exhibiting a metabolic profile distinct from that of AN and similar to that of normal-weight controls. Endothelial dysfunction was observed in both CT and AN, suggesting a potential cardiovascular alteration that warrants further investigation.