RESTING METABOLIC-RATE IN HEALTHY-ADULTS - RELATION TO GROWTH-HORMONESTATUS AND LEPTIN LEVELS

Studies in patients with acromegaly and growth hormone (GH) deficiency , and administration of GH in normal and obese subjects and in patient s with GH deficiency, suggest that GH increases resting metabolic rate (RMR) independently of changes in body composition. To test whether e ndogenous GH status determines RMR, we studied 38 healthy adults (18 w omen and 18 men) in two age groups (young, 30 +/- 0 years (n = 18); ol der, 51 +/- 1 years [n = 18]) with indirect calorimetry, deconvolution analysis of 24-hour GH secretion, arginin stimulation test, insulin-l ike growth factor-I (IGF-I) measurement, lean and fat tissue distribut ion (computed tomography [CT] and dual-energy x-ray absorptiometry), a ssessment of physical fitness (maximal oxygen consumption [VO2max]) th yroid status, and serum leptin levels. RMR was higher in men compared with women, whereas RMR per lean body mass (LBM) (kcal x 24 h(-1) x kg (-1)) was higher in women (30.0 +/- 0.5 v 33.0 2/3 0.8; P = .003). GH secretion was higher in women and in young people. Total-body fat (TBF ) was higher in women, whereas LBM and abdominal fat were higher in me n. Older people had significantly more TBF and abdominal fat as compar ed with younger people. VO2max was higher in younger people. Leptin le vels were higher in women and in older people. Thyroid status was narr owly within the normal range in all subjects. RMR was strongly correla ted with LBM (r = .90, P < .001). RMR/LBM correlated strongly with TBF (r = .49, P < .01) and leptin (r = .56, P < .001), but not with GH st atus. By multiple regression analysis, sex and TBF were the strongest predictors of RMR/LBM. However, in the young subgroup, GH production r ate was a positive determinant of RMR/LBM. In the male subgroup, lepti n was a stronger predictor than TBF of RMR/LBM (P < .001). Neither age , physical fitness, nor thyroid status contributed independently to pr edict RMR/LBM. In conclusion, (1) LBM was the most important determina nt of RMR; (2) RMR/LBM was higher in women and depended strongly on TB F; (3) GH status in healthy adults was only weakly associated with RMR ; and (4) in men, serum leptin levels were a strong positive determina nt of RMR. Copyright (C) 1998 by W.B. Saunders Company.