Contribution of Changes in Body Composition and Adaptive Thermogenesis to the Decline in Resting Metabolic Rate During Prolonged Calorie‐Restricted Weight Loss

Abstract

In the United States, 2 out of 3 adults are overweight or obese. To lose weight, individuals engage in a variety of dietary and exercise interventions. Despite successful weight loss initially, weight loss is typically less than expected and most individuals regain weight. Both phenomena have been linked to a reduction in resting metabolic rate (RMR) secondary to weight loss.ObjectiveTo characterize the independent contributions of changes in body composition, the major predictor of RMR, and adaptive thermogenesis to the observed decline in RMR associated with weight loss. We predict that changes in fat‐free mass and adaptive thermogenesis will both contribute to RMR decline.MethodsSecondary data analysis was conducted on a publically available data set from CALERIE (Comprehensive Assessment of Long‐term Effects of Reducing Intake of Energy), a 2‐year observational calorie restriction study. CALERIE data used for the present analysis examined changes in RMR, body composition, and metabolic hormones over 12 months of 25% calorie restriction in 117 non‐obese (BMI between 22–27.9 kg/m2) men and women with complete data. Changes in RMR were compared between quartiles based on loss of body weight, fat‐free mass, and fat mass. Adaptive thermogenesis was quantified as the reduction in RMR that exceeded the reduction in RMR predicted from changes in organ mass, which was assessed by Dual‐energy X‐ray absorptiometry.ResultsAfter 12 months, mean weight loss was 7.9 ± 0.3 kg (−10.9 ± 0.4%, p<0.001 vs. baseline), and RMR declined by 101 ± 11 kcal/d (−6.8 ± 0.8%, p<0.001 vs. baseline). Individuals who lost the most weight (Q1ΔBW) demonstrated a greater RMR decline than individuals who lost the least weight (Q4ΔBW, p<0.01). The change in RMR did not differ between quartiles based on fat free mass loss (p=0.15), but it was positively associated with the amount of fat loss (p=0.03). In addition, participants who lost the greatest amount of fat mass (Q1ΔFM) exhibited a more pronounced adaptive thermogenic effect (−79 ± 19 kcal/d) than participants with the least amount of fat loss (Q4ΔFM; −10 ± 26 kcal/d, p<0.05 vs. Q1ΔFM). Adaptive thermogenesis was correlated with declines in leptin (r=0.27, p<0.01), T3 (r=0.19, p < 0.05), and insulin (r=0.25, p<0.05).ConclusionsDuring weight loss, the loss of fat mass and adaptive thermogenesis appear to be stronger predictors of RMR decline when compared to the loss of fat‐free mass.Support or Funding InformationThis work was funded in part by the University of Nebraska‐Lincoln McNair Scholars Program and the Undergraduate Creative Activities and Research Experience.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.