Resting metabolic rate, fat-free mass and catecholamine excretion during weight loss in female obese patients

The reduction in resting metabolic rate (RMR) during weight loss exceeds th at accounted for by changes in body composition by 15 %, suggesting that fa ctors other than fat-free mass (FFM) explain the metabolic adaptation durin g food restriction in obesity. Our study aimed to establish if changes in t he sympathoadrenal system activity, as inferred from an integrated measure such as 24 h urinary excretion of catecholamines, may play a role in the RM R adaptation observed during dietary restriction in obese patients. Ninety- three obese female subjects consumed a low-energy diet (LED) (2930 kJ/d (70 0 kcal/d)) for a 3-week period. At the beginning and at the end of the stud y, 24 h urinary excretion of catecholamines, FFM and RMR were measured. The LED induced a significant reduction in body weight (-3.3 (sem 0.4) kg; P < 0.01), FFM (-1.9 (sem 0.7) kg; P < 0.01) and in the fat mass (-1.2 (sem 0. 5) kg; P < 0.01). Noradrenalin excretion (24 h) decreased during the LED fr om 264 (sem 26) during a weight-maintenance period to 171 (sem 19) nmol/24 h after consumption of the LED for 3 weeks (P < 0.001); mean 24 h adrenalin excretion did not change during the LED (22 (sem 3) during the weight-main tenance period v. 21 (sem 3) nmol/24 h after consumption of the LED for 3 w eeks; NS). The LED induced a significant decrease in RMR (7300 (sem 218) v. 6831 (sem 138) kJ/24 h; P < 0.001). The only independent variable that sig nificantly explained variations in RMR both before and after consumption of the LED for 3 weeks, was FFM (r(2) 0.79 and r(2) 0.80 respectively). Urina ry noradrenalin excretion explained a further 4 % of the variability in RMR , but only before the diet, so that a role of sympathoadrenal system on RMR seems to be present in obese patients in basal conditions but not at the e nd of the LED.