DIFFERENCES IN RESTING METABOLIC RATES OF INACTIVE OBESE AFRICAN-AMERICAN AND CAUCASIAN WOMEN

OBJECTIVE: To compare resting metabolic rates (RMR) of African-America n (n = 25) and Caucasian (n = 22) premenopausal (35 +/- 1 y, Mean +/- s.e.m.) women who are obese (95.2 +/- 2.9 kg, body mass index (BMI) = 34.7 +/- 0.9, % body fat = 45.2 +/- 0.9), inactive and free from metab olic disorders or medications that would affect heart rate or RMR. MEA SUREMENTS: RMR and respiratory exchange ratio (RER) by indirect calori metry, body composition by plethysmography, maximal aerobic capacity ( VO2max) and girth measurements. RESULTS: Group mean comparisons were m ade with a Student's t-test or an ANCOVA, which controlled for individ ual differences in body weight and lean body mass (LBM). Significance was set at P < 0.05. Groups were not significantly different in age, h eight, weight, BMI, % body fat, fat mass, RER, VO2max, resting heart r ate, maximal heart rate; or chest, waist, hip, arm, thigh or calf circ umferences. After adjusting for body weight, RMR (IO2/min) for African -Americans (0.254 +/- 0.007) was significantly lower (9%) than for Cau casians (0.277 +/- 0.008). After RMR (IO2/min) was adjusted for LBM, a n even larger difference (-12%) persisted for African-Americans (0.250 +/- 0.008) compared to Caucasians (10.281 +/- 0.008). Predicted RMR ( kJ/d) for the African-Americans was the same as measured RMR, whereas Caucasian women expended about 13% more energy than predicted. When co ntrolling for LBM, the partial correlation between VO2max and RMR was r = 0.51 when VO2max was expressed as l/min, and r = 0.56 when VO2max was expressed as mi O-2/kg/min, both highly significant (P < 0.000). C ONCLUSION: The lower prevalence of obesity in Caucasian women may be d ue in part to a higher RMR as well as an under estimation of RMR in we ight control therapy. Fitness level (VO2max) as well as LBM are signif icant predictors of RMR for both races.