High REE in sumo wrestlers attributed to large organ-tissue mass

Purpose: It is unknown whether high resting energy expenditure (REE) in athletes is attributable to changes in organ-tissue mass and/or metabolic rate. The purpose of this study was to examine the contribution of organ-tissue mass of fat-free mass (FFM) components to REE for Sumo wrestlers who have large FFM and REE. We investigated the relationship between the REE measured by indirect calorimetry and the REE calculated from organtissue mass using a previously published approach. Methods: Ten Sumo wrestlers and 11 male untrained college students (controls) were recruited to participate in this study. FFM was estimated by two-component densitometry. Contiguous magnetic resonance imaging (MRI) images with a 1-cm slice thickness were obtained from the top of head to the ankle joints, and the cross-sectional area and volume were determined for skeletal muscle (SM), liver, kidney, and brain. The volume of adipose tissue, heart, and residual was calculated from each equation. The volume units were converted into mass by an assumed constant density, The measured REE was determined by indirect calorimetry. The calculated REE was estimated as the sum of individual organ-tissue masses (seven body compartments) multiplied by their metabolic rate constants. Results: The measured REE for Sumo wrestlers (2286 kcal(.)d(-1)) was higher (P < 0.01) than for controls (1545 kcal(.)d(-1)). Sumo wrestlers had a greater amount of FFM and FFM components (e.g., SM, liver, and kidney), except for brain. The ratio of measured REE to FFM and the measured REE adjusted by FFM were similar between the two groups. The measured REE values for Sumo wrestlers were not significantly different from the calculated REE values. Conclusions: The high REE for Sumo wrestlers can be attributed not to an elevation of the organ-tissue metabolic rate, but to a larger absolute amount of low and high metabolically active tissue including SM, liver, and kidney.