Effects Of Adiposity And Body Composition On Adjusted Resting Energy Expenditure In Women

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PURPOSE: To compare adjusted resting energy expenditure (REEa) and contributions of skeletal lean mass (SM) and fat mass (FM) to REEa in women at varying levels of adiposity. METHODS: Resting energy expenditure (REE) was measured via indirect calorimetry (REEm). Body composition data was obtained from dual-energy X-ray absorptiometry in 182 female subjects (Mean ± SD; Age 24.2 ± 9.1 yrs, Ht 164.6 ± 6.0 cm, Wt 69.0 ± 22.5 kg, BMI 25.5 ± 8.3 kg·m-2). The sample was divided into tertiles by body fat percent (%fat); Tertile 1 (T1): %fat=18.5-28.4%; Tertile 2 (T2): %fat=28.5-33.8%; Tertile 3 (T3): %fat=34.0-61.0%. To normalize and compare groups, REE was predicted (REEp) to account for differences in FFM and age. Adjusted REE was then calculated from REEm, REEp, and mean REEm per tertile (REEt) using REEa=REEt+REEm-REEp. Contributions (mass × metabolic rate, kcal/kg/day) of FM and SM were calculated as percentages of REEa. One-way ANOVAS and a two-way ANOVA were conducted to analyze differences in body composition and differences between REEm and REEa [(REE (REEm vs REEa) × Group (T1 vs T2 vs T3)], respectively. RESULTS: FM in T3 was significantly higher than T1 (Mean Difference (MD) ± SD; 22.6 ± 25.0 kg, p=0.001) and T2 (MD ± SD; 17.9 ± 25.0 kg, p=0.001). No differences occurred in SM (p>0.05). When evaluating REE and group, there was no significant interaction (p=0.191), or main effect for REE (REEm vs REEa) (p=0.995). There was a significant main effect for group (T1 vs T2 vs T3, p=0.001); REE was significantly higher in T3 versus T1 (MD ± SD; 281 ± 396 kcal/day, p=0.001) and T2 (MD ± SD; 215 ± 396 kcal/day, p=0.001). Expenditure attributed to SM in T1 was significantly higher than T3 (MD ± SD; 3.2 ± 8.6%, p=0.001). Difference in FM contribution between T1 and T2 lacked significance (p=0.210), but T3 had a significantly higher FM contribution than T1 (MD ± SD; 5.1 ± 7.0%, p=0.001) and T2 (MD ± SD: 3.9 ± 7.0%, p=0.001). CONCLUSIONS: Despite similarities in SM, women with elevated %fat experienced lower SM contribution and higher FM contribution to REEa. As adiposity increases, REE increases; FM may explain more of the variance in REE between women of different levels of adiposity.