Bone mass and soft tissue composition in adolescents with anorexia nervosa.

The relationship between bone mass and compartments of soft tissue was studied in 22 adolescent women with anorexia nervosa (mean, 17 years). Results were compared to data on age- and gender-matched controls. Bone mass of the lumbar vertebrae and femoral neck, fat and lean tissue was measured by dual energy X-ray absorptiometry (DXA). Bone mass in the central third of the skeleton, by neutron activation analysis (NAA), and body protein, by prompt gamma ray analysis (PGA), was measured on patients, but not controls. The patients had significantly lower values than controls in total weight (26%), lean tissue (16%), fat (60%), bone mass of lumbar spine (14%), and femoral neck (15%). The mean calcium bone index (CaBI), the central skeletal calcium normalized for body size based on height, was significantly lower than the value for external controls, (0.86 +/- 0.10 vs. 0.97 +/- 0.10). The nitrogen index (NI), body protein normalized for height, showed a similar reduction from external controls (0.84 +/- 0.10 vs. 1.0 +/- 0.10). Bone mass (both DXA and NAA data) was strongly correlated to lean tissue and to protein; the correlations to fat were weaker. Follow-up studies after 7-26 months in 12 patients showed a modest increase in weight (mean, 4.9 kg) which was due, primarily, to an increase in fat with only insignificant increase in lean tissue and in protein. In bone mass, there was either no change or further loss. Only four restored body weight to normal (BMI > 20) and they achieved normal menstruation, but even these four responders showed no increase in bone mass. Our studies confirm that adolescent females with anorexia nervosa suffer losses not only in all compartments of body composition, but also demonstrate that the restoration of bone mass lags behind improvement in soft tissue compartments. These results were independent of methods used for the measurements.