Gender Variations In The Relationship Between Anthropometric Variables, Percent Fat, And Resting Metabolic Rate

Resting metabolic rate (RMR) accounts for most of daily energy expenditure. Body mass index (BMI), waist circumference (WC), waist to height ratio (WHtR), and percent body fat (%BF), are related to RMR. PURPOSE: To determine if gender variations exist in the relationships between BMI, WC, WHtR, %BF, and RMR. METHODS: Fifty-four (27M, 27F) volunteers (age M = 22.9 ± 6.5, F = 22.2 ± 6.2 years) had height (Ht), mass, WC, %BF, and RMR measured. BMI was calculated by dividing mass (kg) by the square of Ht (m). WC was measured with a measuring tape at the narrowest part of the trunk. WHtR was calculated by dividing WC by Ht. RMR was measured using a metabolic cart measuring oxygen consumption and carbon dioxide production. Percent fat was measured using air displacement plethysmography. RMR relative to body mass (RMR/kg) was measured by dividing RMR by mass. Pearson product-moment correlations were used to analyze the results. RESULTS: Means and standard deviations were: Ht (M) 178.7 ± 7.1 cm, (F) 163.6 ± 8.0 cm; Mass (M) 86.8 ± 15.8 kg, (F) 69.2 ± 16.2 kg; RMR (M) 2094 ± 400.9 kcals/d, (F) 1480 ± 295.2 kcals/d; BMI (M) 27.3 ± 5.6 kg/m2, (F) 25.7 ± 4.8 kg/m2; WC (M) 86.7 ± 12.1 cm, (F) 76.5 ± 10.8 cm; WHtR (M) 0.49 ± 0.08, (F) 0.47 ± 0.06; RMR/kg (M) 24.4 ± 4.3 kcals/d, (F) 21.8 ± 4.4 kcals/d; and %BF (M) 19.0 ± 10.1, (F) 31.6 ± 9.7 %. Correlations between RMR and the anthropometric variables (AV) were: BMI (M) r = 0.59, R2 = 0.35, (F) r = 0.38, R2 = 0.15; WC (M) r = 0.58, R2 = 0.33, (F) r = 0.48, R2 = 0.23; WHtR (M) r = 0.56, R2 = 0.31, (F) r = 0.31, R2 = 0.10; and %BF (M) r = 0.52, R2 = 0.27, (F) r = 0.33, R2 = 0.11. Correlations between RMR/kg and the AV were: BMI (M) r = -0.29, R2 = 0.09, (F) r = -0.54, R2 = 0.29; WC (M) r = -0.22, R2 = 0.05, (F) r = -0.46, R2 = 0.21; WHtR (M) r = -0.14, R2 = 0.05, (F) r = -0.46, R2 = 0.20; and %BF (M) r = -0.08, R2 = 0.01, (F) r = -0.48, R2 = 0.23. CONCLUSIONS: For both genders, results indicate weak to moderate correlations between both absolute and relative RMR, the AV, and %BF. These positive relationships indicate larger people have higher RMR. The inverse relationships between RMR/kg and AV and %BF suggest lower metabolic rates per unit of mass and metabolically active tissue in those with higher levels of body fatness. These inverse relationships were stronger for females than males. Further research is necessary to discern the reason for these differences.