Adipocyte fatty acid binding protein (A-FABP) has been suggested to play an important role in fat metabolism linking obesity and the metabolic syndrome. Increasing A-FABP plasma levels were observed during greatest weight loss after bariatric surgery suggesting that A-FABP may indicate changes in fat mass in dynamic situations. As there are no data on weight gain, we investigated the effect of refeeding anorexic patients on body composition and A-FABP plasma levels. Parameters of glucose and lipid metabolism as well as plasma levels of leptin and A-FABP were prospectively assessed in 16 female patients with anorexia nervosa during inpatient weight restoration. Body composition was determined by multifrequency body impedance analysis. After 28 days, fat mass increased from 4.4 +/- 2.5 kg at baseline to 5.5 +/- 2.2 kg (P < 0.01), constituting 40% of total weight gain. Conversely, A-FABP concentrations decreased from 32.56 +/- 35.59 ng/ml at baseline to 21.27 +/- 13.68 ng/ml (P < 0.05), which corresponds to a significant decrease in the proportion of A-FABP per kilogram fat mass from 7.86 +/- 5.23 to 4.09 +/- 2.12 ng/ml/kg (P </= 0.001). Variation in A-FABP plasma concentration was predictive for changes in total cholesterol levels (adjusted r (2) = 0.239; P < or = 0.05), but not for gain in weight, fat mass, or percent body fat. The present results indicate that variation in A-FABP plasma levels reflect alterations in nutritional status in patients with anorexia nervosa.