Influence of adiposity on tonic sympathetic support of resting metabolism in healthy adults

BACKGROUND: beta-Adrenergic receptor sympathetic nervous system (beta-AR SNS) support of resting metabolic rate (RMR) is attenuated with older age, female sex, and a sedentary lifestyle. Total and abdominal adiposity and/or body fat pattern modulate some SNS-mediated physiological functions. OBJECTIVE: To determine if total and abdominal adiposity and/or body fat distribution are independently related to SNS support of RMR. DESIGN: Cross-sectional comparison of beta-AR SNS support of RMR. SUBJECTS: A total of 54 healthy male and female subjects aged 18-75 y. MEASUREMENTS: RMR (ventilated hood, indirect calorimetry) before (baseline) and during complete beta-AR blockade; body composition by dual energy X-ray absorptiometry. RESULTS: Forward stepwise multiple regression analysis using sex, exercise status, age group, %body fat, total adiposity, abdominal adiposity, and the ratio of abdominal adiposity to hip adiposity as variables revealed sex to be the strongest predictor, explaining 21% of the variability in beta-AR SNS support of RMR (P=0.0006). Age group explained an additional 4% and exercise status a further 4% (both P=0.10). %Body fat, total adiposity, abdominal adiposity, and the ratio of abdominal adiposity to hip adiposity did not enter the equation. CONCLUSION: Total and abdominal adiposity and body fat pattern are not independent physiological determinants of beta-AR SNS support of RMR among healthy men and women. Moreover, further support is provided for our previous finding of attenuated beta-AR SNS support of RMR with age, female sex, and sedentary lifestyle.