Small organs with a high metabolic rate explain lower resting energy expenditure in African American than in white adults2

• Published in: The American journal of clinical nutrition 2006-05, Vol.83 (5), p.1062-1067
• Main Authors: Gallagher, Dympna, Albu, Jeanine, He, Qing, Heshka, Stanley, Boxt, Lawrence, Krasnow, Norman, Elia, Marinos
• Format: Article
• Language: English
• Subjects: African Americans; ethnicity; fat-free mass; magnetic resonance imaging; metabolism; organs; Race; resting energy expenditure; tissues; whites
• ISSN: 0002-9165
• DOI: 10.1093/ajcn/83.5.1062

Background:African Americans have a lower resting energy expenditure (REE) relative to fat-free mass (FFM) than do whites. Whether the composition of FFM at the organ-tissue level differs between African Americans and whites and, if so, whether that difference could account for differences by race in REE are unknown. Objective:The objectives were to quantify FFM in vivo in women and men at the organ-tissue level and to ascertain whether the mass of specific high-metabolic-rate organs and tissues differs between African Americans and whites and, if so, whether that difference can account for differences in REE. Design:The study was a cross-sectional evaluation of 64 women (n = 34 African Americans, 30 whites) and 35 men (n = 8 African Americans, 27 whites). Magnetic resonance imaging measures of liver, kidney, heart, spleen, brain, skeletal muscle, and adipose tissue and dual-energy X-ray absorptiometry measures of fat and FFM were acquired. REE was measured by using indirect calorimetry. Results:The mass of selected high-metabolic-rate organs (sum of liver, heart, spleen, kidneys, and brain) after adjustment for fat, FFM, sex, and age was significantly (P < 0.001) smaller in African Americans than in whites (3.1 and 3.4 kg, respectively; x̄ ± SEE difference: 0.30 ± 0.06 kg). In a multiple regression analysis with fat, FFM, sex, age, and race as predictors of REE, the addition of the total mass rendered race nonsignificant. Conclusions:Racial differences in REE were reduced by >50% and were no longer significant when the mass of specific high-metabolic-rate organs was considered. Differences in FFM composition may be responsible for the reported REE differences.