Objective: To compare measured resting energy expenditure (REE) with that predicted by formulas derived from populations with normal weight or obesity and from women with severe and morbid obesity.
Material and methods: 66 women (aged 35.6 +/- 10.3 y and BMI of 44.7 +/- 4.9 kg/m2) were evaluated by indirect calorimetry with a metabolic monitor Deltatrac (Datex Inst., Finland), before undergoing gastric bypass. REE was calculated with the following equations: Harris-Benedict's with both actual and adjusted weight, Ireton-Jones', Mifflin's, and Carrasco's Fast Estimation, which corresponds to 16.2 kcal x kg actual weight.
Results: (mean +/- sd). Measured REE was 1797 +/- 239 kcal/day. All formulas, except Harris-Benedict's with adjusted weight, overestimated REE. The Ireton-Jones' equation presented the greater overestimation (689 +/- 329 kcal/day), whereas Mifflin's equation overestimated REE only by 6 +/- 202 kcal/day. No significant differences were detected between measured and calculated REE by Mifflin's and Carrasco's Fast Estimation. Accuracy (defined as difference between calculated and measured REE within +/- 10%) was greater with Mifflin's equation (68%), followed by Harris-Benedict's with actual weight (64%) and Carrasco's Fast Estimation (61%). By using the Bland-Altman analysis, significant correlations were observed between calculated-measured REE and mean REE (calculated + measured/2) with all equations except Carrasco's Fast Estimation. This means that all but one formula underestimate or overestimate REE depending on the level of measured REE.
Conclusion: In severe and morbid obese women, Mifflin's and Carrasco's Fast Estimation equations provided the best performance to estimate REE. Before recommending an equation in an a subset of individuals it is necessary to make previous validation studies to determine that equation with the best predictive power for this particular group of patients.