Calculation of Energy Expenditure in Women Using the MET System

PURPOSE: Interpretation of physical activity as energy expenditure requires adjustment for body size. This is usually accomplished by means of the MET system, which assumes a basal metabolic rate (BMR) of 4.184 kJ.kg(-1).h(-1) and, when the standard calculation is used, that the energy costs of different activities are proportional to BMR. These relationships may be altered by increases in percent total body fat (% TBF), and this paper examines relationships between % TBF and total energy expenditure (TEE) obtained using the standard and a proposed calculation. METHODS: Published data regarding body composition, physical activity (heart rate recording), and BMR in 11 American women (before and after weight gain) and in 15 Swedish women (before and during pregnancy) were used to calculate TEE. Reference estimates of TEE were obtained using doubly labeled water. RESULTS: In Swedish women, reference TEE minus standard TEE (MJ.24 h(-1)) was 1.37 +/- 1.29 (P 0.05) and 0.31 +/- 1.28 (P > 0.05) (MJ.24 h(-1)), respectively. In American women before and after weight gain, reference TEE minus standard TEE (MJ.24 h(-1)) were 0.38 +/- 1.79 (P > 0.05) and 1.39 +/- 2.36 (P > 0.05), respectively, whereas the corresponding differences for proposed TEE (MJ.24 h(-1)) were -0.52 +/- 2.20 (P > 0.05) and 0.21 +/- 2.36 (P > 0.05), respectively. In Swedish women before pregnancy and American women after weight gain (N = 26, BMI = 18-39), significant (P < 0.001) relationships were found for standard TEE/proposed TEE (y) versus % TBF, (x, r = -0.65) and versus BMI (x, r = -0.70). CONCLUSIONS: : In individuals with a TBF content typical for contemporary Western women, standard TEE is lower than proposed TEE. This bias increases as the TBF content of subjects increases. The results indicate that proposed TEE is more accurate than standard TEE, but this requires confirmation.