Assessment Of Racial And Ethnic Differences In Inferred Energy Expenditure Using Nationally Representative Data
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DepartmentPublic Health and Policy
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Evolution & Development
Nun Sava-Siva Amen-Ra, Dr.PH, December 2011 Dissertation Chair: H. Eduardo Velasco, M.D., M.Sc., Ph.D. Department of Public Health Analysis As assessed by body mass index (BMI) African Americans exhibit higher rates of obesity than Caucasian Americans. Bodyweight is influenced principally by energy intake, voluntary energy expenditure (i.e. exercise) and basal metabolic rate (i.e. resting energy expenditure). Resting energy expenditure is, in turn, influenced by physiological factors that are largely (though not entirely) innate and therefore less amenable to alteration. Existing observational evidence indicates that Blacks exhibit lower resting energy expenditure than Whites. The present study sought to confirm this finding for the first time using nationally representative data. We hypothesized that other ethnicities and multiracial persons would, as a consequence of exhibiting an amalgam of Africoid and Europoid metabolic traits, exhibit an average resting energy expenditure intermediate between Blacks and Whites. We confirmed that Blacks exhibit lower resting energy expenditure than Whites--a difference of approximately 150 to 300 fewer kilocalories per day. This finding was significant in each permutation of our analysis--from the simple association of race and resting energy expenditure to our final regression model adjusted for common confounders (i.e. age, gender, income, and education), body fat content, diabetes, thyroid dysfunction, and weight loss in previous year. Further, we found that energy intake did not differ significantly between Blacks and Whites whereas Blacks were found to expend significantly more energy voluntarily than Whites. Blacks and Whites did not differ significantly in bodyweight, though Blacks were found to be leaner than Whites as evidenced by significantly lower body fat content in the former. Given their relatively low level adiposity, environmental factors such as stress ineluctably emerge as plausible explanatory postulates in disparate disease susceptibility among African Americans. Our findings further suggest that if rates of obesity are to be reduced in African Americans, recommendations would need to encourage lower levels of average energy intake than extant in the general populace and higher levels of activity energy expenditure than extant in the general populace. In short, African Americans would need to adopt more austere lifestyle regimens relative to the general populace in order to reduce their rate of obesity below present levels. Our finding that adiposity (as assessed by X-ray absorptiometry) is significantly lower in Blacks than Whites suggests that conventional classifications of adiposity based on such indirect measures as body mass index may be less applicable in African Americans presumably due to racial/ethnic differences in body composition. Lastly, our findings accord with theories of human evolution which posit that metabolic adaptations to environmental alteration entailing increased energy efficiency were essential to the survival of the human species.