Accuracy of prediction equations for calculating resting energy expenditure in morbidly obese patients

Abstract

Introduction: The accuracy of prediction equations for estimating resting energy expenditure (REE) in morbidly obese patients is unclear. The aim of this study was to compare the REE measured using bedside indirect calorimetry with commonly used prediction equations. Methods: A total of 31 morbidly obese patients were studied. Pre-operative REE was measured with indirect calorimetry and compared with estimated REE using the Harris-Benedict and Schofield equations. All patients subsequently underwent a Roux-en-Y gastric bypass and measurements were repeated at six weeks and three months following surgery. Results: The mean age of the patients was 47 years. The mean pre-operative body mass index was 46kg/m2. The mean REE measured using indirect calorimetry was 1,980kcal/day. The estimated REE using the Harris-Benedict and Schofield formulae was 2,195 and 2,129kcal/day respectively. The equations overestimated REE by 10% and 7%. Body weight and body mass index reduced significantly following Roux-en-Y gastric bypass. There was no significant change in measured REE over the three-month period. After weight loss the difference between the estimated and measured REE reduced to 1-3%. Conclusions: Prediction equations overestimate REE in morbidly obese patients. Their accuracy improved after surgery induced weight loss, confirming their validity for the normal weight population. Indirect calorimetry should be used in morbid obesity.