Abstract 13109: Phenotyping Fat but Fit: Insights From Cardiac Structure and Adiposity Imaging in the Dallas Heart Study.

Obesity and decreased cardiorespiratory fitness (CRF) are independent risk factors for mortality, but higher CRF may minimize the adverse impacts of obesity. Using deep phenotyping, we explored what blood-based and imaging biomarkers were associated with higher CRF among both non-obese and obese individuals in a large multiethnic epidemiological cohort to better understand the biology of the fat but fit phenotype. We performed a cross-sectional analysis of participants enrolled in the Dallas Heart Study between 2007 to 2009 without cardiovascular disease, HIV, cancer, or end-stage renal disease. A total of 2351 individuals were divided into four groups by obesity status (BMI < or ≥30 kg/m2) and CRF (unfit or fit defined as >25th percentile by age and sex, measured using a submaximal treadmill test). Multivariate logistic regression analyses were used to compare circulating biomarkers of cardiometabolic risk, cardiac structure by cardiac magnetic resonance, and adipose depots by dual-energy X-ray absorptiometry between these groups. There were 1052 non-obese and fit, 227 non-obese and unfit, 716 obese and fit, and 356 obese and unfit persons. After adjustment for sex, race, and BMI, factors that were independently associated with fitness in the obese group (versus obese and unfit group) were lower pulse rate (OR, 0.56; 95% CI 0.44-0.71), higher end-diastolic volume indexed to body-surface-area (OR, 1.37; 95% CI 1.06-1.77), and lower subcutaneous fat indexed to body-surface-area (OR, 0.57; 95% CI 0.34-0.96). Lower pulse rate and subcutaneous fat were also associated with being more fit in the non-obese; but contrary to the obese, no cardiac structural measures were statistically significant. These findings suggest that the fat but fit phenotype is characterized by a lower resting pulse, less subcutaneous fat, and a higher left ventricular end-diastolic volume. Being fit is linked to beneficial physiological and cardiovascular changes, irrespective of BMI. [ABSTRACT FROM AUTHOR]