Body composition changes in anorexia nervosa

To assess the body composition changes in anorexia nervosa and after medium term recovery.

A descriptive study.

Rome, Italy.

Twenty women affected by anorexia nervosa (AN) with a BMI [weight (kg)/height (m2)] below 17 kg/m2 and weight-stable for at least three months, were compared with 10 well nourished control women (CO) and nine rehabilitated subjects (R-AN), who had a BMI above 18.5 kg/m2 stable for at least the last six months.

Body fat was assessed by underwater weighing, muscle mass by urinary creatinine, total body water (TBW) by impedance parameters (50 kHz and 800 microA), skeletal mass by anthropometry and radius bone mineral density by dual photon absorptiometry in ultra-distal (UD-BMD) and medio-distal (MD-BMD) sites.

The AN group, as compared to the control group, had a significantly lower weight, body mass index (BMI kg/m2) and percent body fat (P < 0.0000). Creatinine urinary excretion was lowest in absolute term and when expressed as creatinine height index or per kg fat free mass (FFM) (P < 0.0000); muscle mass per kg body weight was 13% lower (P < 0.01). Ultra distal bone mineral density (UD-BMD) was 6% lower (not significant). TBW as percent of body weight was significant higher (P < 0.001): however TBW/FFM % was not statistically different with large inter-individual variability. An altered distribution of extra and intra-cellular water was suggested by the phase angle (AN: 4.4+/-0.8 degrees; CO: 6.1+/-0.4 degrees; (P < 0.0000). In rehabilitated anorexic patients (R-AN) the fat mass represented 53% of the weight gain. Their creatinine excretion remained still below the mean value of the controls (P < 0.001). The impedance parameters were not significantly different between the R-AN and the CO groups, however, the phase angle of the R-AN (5.0+/-0.7 degrees) remained lower than in the CO group, indicating that the water distribution was still altered.

This study shows that AN is a condition of reduced body fat as well as of muscle mass, with a slightly reduced bone mass. In the course of rehabilitation, most of the weight regained is represented by fat, while the muscle mass appears to lag behind, at least in the medium term.