Abstract P293: Resting Metabolic Rate, Cardiorespiratory Fitness, and Racial Differences in Adiposity among Adult Women

Abstract

Background: African American (AA) adult females have a higher prevalence of overweight and obesity compared to their Caucasian (Cauc) peers. Lower resting metabolic rate (RMR) values, a hypothesized contributor to higher levels of adiposity, have been observed among AA women. However, it is unknown whether cardiorespiratory fitness (CRF) is associated with RMR in this population. Methods: Sixty-two overweight/obese (body mass index [BMI] ≥25.0) yet healthy women (42 Cauc, 20 AA) between the ages of 21-35 years were recruited for the present study. RMR was measured using a ventilated hood system. Participants arrived fasted for at least 12 hrs and having refrained from alcohol/exercise for at least 24 hrs. Participants rested in a supine position for 30-minutes, followed by a 30-minute RMR gas collection period. Body weight (BW) and height were measured and body fat (BF) was calculated as the percentage of total weight identified as fat tissue by dual x-ray absorptiometry. CRF was measured via a metabolic cart during a modified Bruce treadmill protocol. Total energy expenditure (TEE) was assessed using an arm-based physical activity monitor worn at all times for 10 consecutive days. Energy intake (EI) was assessed over a 14-day period via interviewer-administered dietary recall. Results: Cauc and AA participants were similar in terms of age (27.6±4.2 years), weight (79.9±9.9 kg), BMI (29.4±2.9 kg/m2), body fat percentage (41.0±5.1 percent), and EI (1760±397 kcal/day). Compared to Cauc, AA women were slightly shorter (162.4±7.0 vs. 165.8±5.1 cm, p=0.0371), lower CRF (27.4±3.8 vs. 31.4±5.2 ml/kg/min, p=0.0032), lower TEE (2438±264 vs. 2598±303 kcal/day, p=0.0102) and lower RMR (1436±222 vs. 1569±181 kcal/day, p=0.0154). Energy expenditure resulting from moderate/vigorous activity was higher in Cauc females (552±386 vs. 355±197 kcal/day, p=0.0102). RMR was correlated with fat mass, CRF and race. After adjustment for age, race, body weight, fat-free mass, fat mass, and CRF, the least squares means for RMR remained lower in AA compared to Cauc (1444 vs. 1565 kcal/day, p=0.0034) and was only significantly related race (p=0.0034). Conclusion: The results of this study confirm previous research reporting lower RMR values among AA females compared to their Cauc counterparts, though these differences did not result in variations of adiposity. The current analyses suggest CRF plays an important role in the determination of RMR. The differences among racial groups in energy expenditure resulting from moderate/vigorous activity may play a key role in the determination of CRF and ultimately RMR.