CHANGES IN FAT-FREE MASS IN OVERWEIGHT PATIENTS WITH RHEUMATOID-ARTHRITIS ON A WEIGHT REDUCING REGIMEN - A COMPARISON OF 8 DIFFERENT BODY-COMPOSITION METHODS

The aim of this work was to compare and validate seven different metho ds for estimating changes in fat free mass, in patients suffering from rheumatoid arthritis. Measurements were made of fat and fat free mass before and after 12 weeks on an energy restricted, protein rich diet and physical training. The subjects were sixteen female and three male overweight out-patients (mean body mass index at baseline: 30 kg/m(2) ) suffering from rheumatoid arthritis, according to the criteria of th e American Rheumatism Association. Fat free mass was estimated by eigh t different body composition methods (a four-compartment model, total body water, total body potassium, impedance, near infrared interactanc e, creatinine excretion, body mass index and skinfold measurements). M ean weight loss was 2.7 kg fat and 1.7 kg fat free mass. There was no difference between measurements of mean change in fat free mass by the four-compartment model and the other methods, except for the creatini ne method (P = 0.03). Compared to the four-compartment method, the tot al body water method gave the most accurate estimate of individual fat free mass changes (residual Mean Square: 0.4 kg), second to this meth od, the impedance method, seemed most valid (residual Mean Square: 0.8 kg). Accuracies of the other methods were lower (residual Mean Square between 1.8 and 19.0 kg). Of eight methods for estimating changes in FFM, the TBW method gave the most accurate estimate of individual FFM changes, compared to a four-compartment model used as reference. None of the other methods were valid for estimating changes in FFM on an in dividual level. Estimation of individual changes in fat free mass by m ost methods may not be sufficient for clinical purposes.