Nitrogen loss and urinary creatinine excretion during fasting in massive obesity.

Six (5 f, 1 m) massively obese, otherwise healthy subjects, were submitted for 4 weeks to a very-low-calorie diet (VLCD): 80 kcal, 335 kJ = 2.6 g N/day (17 g protein, 0 CHO and fat). Daily urinary creatinine excretion (UCE) and weekly nitrogen loss (NL) were determined during the whole period of treatment. Both NL and UCE decreased from the second week of treatment indicating a progressive sparing effect on lean body mass (LBM). A positive correlation (r = 0.991, P less than 0.001) was observed between mean daily UCE and NL, indicating that NL during prolonged fasting in obesity is possibly influenced by the lean body mass of the individual.