Specific metabolic rate and body weight regulation: racial and ethnic differences in mass-independent energy expenditure

Purpose: We evaluated inter-individual differences in adjusted energy expenditure (EE) during 24 hours of carefully controlled energy balance conditions in an ethnically diverse cohort and tested whether the relationship between adjusted EE and free-living weight change at 1 year differed by race/ethnicity. Methods: Healthy individuals (n=120: 20 Black participants, 37 Whites, 46 Indigenous Americans, 17 Hispanics) had 24-h EE measured in a whole-room indirect calorimeter during eucaloric conditions and adjusted for DXA-derived body composition and other covariates. Results: Black participants had ~335 kJ/day (~80 kcal/day) lower adjusted 24-h EE (adj24hEE) compared to other groups, reflecting a 20% lower adjusted metabolic rate after accounting for body composition and other known EE determinants. Black participants reported lower mean perceived hunger, dietary disinhibition, and perceived stress. Among fifty-six individuals (including only 11 Black participants) whose free-living weight change was assessed at 1 year, a 1 MJ/day (~239 kcal/day) higher adj24hEE at baseline predicted a mean weight gain of 3.8 kg only in those who did not identify as Black, whereas adj24hEE tended to be inversely associated with 1-year weight change in Black participants (race/ethnicity interaction: p=0.02). Given the small subgroup sizes, particularly for Black participants, these interaction findings should be considered exploratory and hypothesis-generating. Conclusion: Relative metabolic rate differs between races/ethnicities and may differentially predict future weight change, although the race-specific interaction findings require confirmation in larger cohorts. For individuals who do not self-identify as Black, relatively higher metabolic demands during sedentary conditions may contribute to energy sensing-mediated overeating and ultimately weight gain.