Urinary 3-methylhistidine excretion: association with total body skeletal muscle mass by computerized axial tomography.

BACKGROUND The urinary excretion of endogenous 3-methylhistidine (3-MH) has been proposed as a predictor of skeletal muscle mass (SM). In this study, we report the relationship between 24-hour urinary 3-MH excretion and SM. METHODS Total body SM was measured by multiscan computerized axial tomography (CT) in a sample of 10 healthy adult men who followed a meat-free diet for 7 days. 3-MH was measured during the last 3 days of the meat-free diet protocol on consecutive 24-hour urine collections. RESULTS The 3-MH excretion was 216.3 +/- 44.7 mumol/d (mean +/- SD) and was found well associated with SM (in kilograms), SM = 0.0887 x 3-MH + 11.8; r = .88, p < .001. Compared with CT, the previous 3-MH-SM prediction equation suggested by Lukaski et al underestimated SM by an average of 8.9 kg in the 10 healthy men. This difference was caused by the Burkinshaw-Cohn neutron activation model, which underestimated SM and was used as the reference in the Lukaski method. CONCLUSIONS Twenty-four-hour urinary 3-MH excretion can be applied for estimating SM in healthy adult men on a meat-free diet.