Creatinine excretion over 24 hours as a measure of body composition or of completeness of urine collection.

Continuous collections of urine for up to 3 weeks from obese patients on a meat-free low-energy diet showed fluctuations in creatinine excretion so that the coefficient of variation was 8.7-34.4 per cent. Urine creatinine excretion was poorly correlated with measures of lean body mass such as density, body water or body potassium. Under the conditions of our study creatinine excretion is not a reliable indicator of either lean body mass nor the completeness of urine collection. We also conclude that the increased lean body mass in obese women contains a relatively small proportion of muscle.