Short-term effects of a hypocaloric diet on nitrogen excretion in morbid obese women

Objective: To determine whether the daily pattern of urine excretion of N w astes is affected by obesity and very low-calorie diets (VLCD). Design: The plasma amino acid, urea and other energy parameters, as well as the urinary excretion of total nitrogen, urea and creatinine were studied in obese and normal-weight women. The obese women's data were obtained unde r hospital basal controlled conditions (8.1 MJ/day) and after 3 days of VLC D diet (1.9 MJ/day) controls were studied only once (5.8 MJ/day). The hourl y excretion patterns of total N, urea and creatinine were determined from t he composition of each bladder voiding. Subjects: Twenty morbidly obese and 10 age-matched normal-weight control wo men. Results: Plasma amino acid levels were higher in obese women, which showed a limited ability to metabolize amino acid hydrocarbon skeletons. Neither d ifferences in the patterns between groups nor total 24h values for urine vo lume were found. Total N and urea excretion diminished under VLCD diet. Hou rly creatinine excretion showed a flat pattern and was higher in obese wome n than in the controls, VLCD diet diminished the amount of creatinine excre ted in 24h. Conclusions: The early change in energy availability that the creatinine ex cretion figures reflect may result from the energy conservation mechanisms induced in response to energy restriction. The early onset of this effect ( 3 days, and the extent of decrease (similar to 19%) also suggest that the i mpact of VLCD on the muscle energy budget of the obese is more marked than usually assumed.