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Differences between brain mass and body weight scaling to height: potential mechanism of reduced mass-specific resting energy expenditure of taller adults

Steven B. Heymsfield,¹ Thamrong Chirachariyavej,^3, Im Joo Rhyu,⁴ Chulaporn Roongpisuthipong,² Moonseong Heo,⁵ and Angelo Pietrobelli⁶

¹Global Center for Scientific Affairs, Merck & Company, Rahway, New Jersey; Departments of ²Medicine and ³Pathology, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand; ⁴Department of Anatomy, College of Medicine, Korea University, Seoul, Korea; ⁵Department of Epidemiology and Public Health, Albert Einstein College of Medicine, Bronx, New York; ⁶Pediatric Unit, Verona University Medical School, Verona, Italy

Submitted 21 August 2008 ; accepted in final form 11 November 2008

Adult resting energy expenditure (REE) scales as height^1.5, whereas body weight (BW) scales as height². Mass-specific REE (i.e., REE/BW) is thus lower in tall subjects compared with their shorter counterparts, the mechanism of which is unknown. We evaluated the hypothesis that high-metabolic-rate brain mass scales to height with a power significantly less than that of BW, a theory that if valid would provide a potential mechanism for height-related REE effects. The hypothesis was tested by measuring brain mass on a large (n = 372) postmortem sample of Thai men. Since brain mass-body size relations may be influenced by age, the hypothesis was secondarily explored in Thai men age 45 yr (n = 299) and with brain magnetic resonance imaging (MRI) studies in Korean men (n = 30) age 20<30 yr. The scaling of large body compartments was examined in a third group of Asian men living in New York (NY, n = 28) with MRI and dual-energy X-ray absorptiometry. Brain mass scaled to height with a power (mean ± SEE; 0.46 ± 0.13) significantly smaller (P < 0.001) than that of BW scaled to height (2.36 ± 0.19) in the whole group of Thai men; brain mass/BW scaled negatively to height (–1.94 ± 0.20, P < 0.001). Similar results were observed in younger Thai men, and results for brain mass/BW vs. height were directionally the same (P = 0.09) in Korean men. Skeletal muscle and bone scaled to height with powers similar to that of BW (i.e., 2–3) in the NY Asian men. Models developed using REE estimates in Thai men suggest that brain accounts for most of the REE/BW height dependency. Tall and short men thus differ in relative brain mass, but the proportions of BW as large compartments appear independent of height, observations that provide a potential mechanistic basis for related differences in REE and that have implications for the study of adult energy requirements.

body composition; nutritional requirements