VISCERAL FAT METABOLIC RATE AND CHD RISK IN YOUNG ADULTS

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The prevalence of obesity increased markedly in the United States from the l960's to the 1980's, and varies by race and gender with particularly high rates of obesity among black women. Reasons for the ethnic differences in the prevalence of obesity are not understood. This is a proposal for a cross-sectional study to be performed in conjunction with the 10-year follow-up examination for the Coronary Artery Risk Development in Young Adults (CARDIA) study, an NHLBI-funded longitudinal study of development of risk factors for coronary heart disease (CHD) in young black and white adults. We propose to measure visceral (intraabdominal) fat by computerized tomography (CT) scan and to measure resting metabolic rate by indirect calorimetry in 400 CARDIA subjects, ages 28-40 years (100 of each race/gender group) from the Oakland, California and Birmingham, Alabama centers. Using these data, we will test the hypothesis that visceral adipose tissue, the component of fat considered to be most strongly related to CHD risk factors, differs in black and white subjects. Specifically, we propose that black subjects will have less visceral adipose tissue for a given level of total body fat than will white subjects. Further, the relationship between visceral adipose tissue and risk factors for CHD should be similar in all subjects. This would explain the different relationship between obesity and CHD risk factors seen in black vs white subjects. A second specific aim is to determine whether black women have a lower resting energy expenditure than black men or whites. This could explain the higher prevalence of obesity in black women than in black men or whites of either gender. CT scans will be recorded on tape and shipped to the University of Colorado Health Sciences Center where visceral adipose tissue will be quantified. Dietary intake and physical activity will be measured as important covariates in the relationship between metabolic rate and adiposity, and thyroid function will be measured as a determinant of resting energy expenditure. The CARDIA study will provide funding for cardiovascular risk factor measurements, including blood pressure, lipids, insulin, glucose, smoking, and anthropometric measurements including dual energy absorptiometry (DEXA) measurements of total and regional body fat. This study represents a unique opportunity to investigate factors that may influence the development of obesity, to better understand the relationship between obesity and cardiovascular risk factors, and to increase understanding of racial differences in adiposity.