Relationship between fat-free weight and urinary 3-methythistidine excretion in man.

The relationship between body composition determined by densitometry and urinary 3-methylhistidine (3-Mehis) output was studied in 16 healthy men (range 23--52 yr) who consumed a self-selected meat-free diet for 3 days and collected a 24-hr urine sample on the third day. Urinary 3-Mehis and creatinine outputs were 225 +/- 8 mumoles/day (mean +/- SEM) and 1.6 +/- 0.1 g/day, respectively. Mean fat-free weight (FFW) was 61.5 kg (range 46.9--76.4 kg). FFW correlated more closely with urinary 3-Mehis excretion (r = 0.89, p < 0.001) than with urinary creatinine excretion (r = 0.67, p < 0.1). These results suggest that endogenous urinary 3-Mehis may be related to muscle weight, which is a major component of FFW.