Background and objective: The aim of this study was to evaluate the currently available predictive equations for basal metabolic rate (BMR) in subjects with obesity class II and III, and to assess the contribution by the components of a two-compartment model of body composition, namely the lean body mass (LBM) and the fat mass (FM) to the prediction. A second objective was to examine the reliability of the Harris Benedict equation in obese subjects, especially with a weight > or = 120 kg.
Patients and methods: In 43 patients (age range 18 to 61 years, 5 men, 38 women) with obesity class II and III (body mass index, BMI, mean +/- SD 45.6 kg/m2 +/- 5.4 kg/m2, range 37.1-58.6 kg/m2) basal metabolic rate BMR was determined using indirect calorimetry (Deltatrac MBM, Datex, Instrumentarium Corp., Helsinki, Finnland) and the components of body composition were determined using the bioelectrical-impedance-analysis (BIA) method (BIA, Akern-Gerät, RJL Systems, Detroit). Calculated BMR was compared with measured BMR.
Results: The best fitting equations for predicting BMR in these 43 severe und morbidly obese subjects were the Harris-Benedict (ratio calculated BMR to measured, BMR mean +/- SD%; correlation coefficient r = 101 +/- 12.9; 0.69), the Jensen (101.5 +/- 12.3; 0.74), the Nelson (99.3 +/- 11.4; 0.76) and the Cunningham equation (98.9 +/- 11.7; 0.74). The predictive value of the original Harris-Benedict equation was slightly different from modified Harris-Benedict equation, which was recalculated by Roza et al. (101.1 +/- 12.9; 0.69 vs. 99.7 +/- 12.8; 0.69). In the group of the 22 subjects with a body weight > or = 120 kg ratio of estimated values for BMR using original Harris-Benedict equation to measured BMR was 102.2 +/- 15.4% (mean +/- SD%, r = 0.61), respectively 93.2 +/- 14.5% (r = 0.50) when weight was set at 120 kg due to current recommendations. The ratio calculated BMR/measured BMR according to the Nelson equation in this subgroup was 101.0 (12.1/0.74).
Conclusion: In patients with obesity class II and III the equation of Harris-Benedict predicted the average BMR with acceptable precision for clinical use and was better fitting than most of the currently available predictive equations for basal metabolic rate (BMR). However, the recalculated version (by Roza et al.) was more accurate and should therefore be used instead of the original equation: BMR (men) = 88.362 + 4.799 x (length) + 13.397 x (weight) - 5.677 x (age); BMR (women) = 447.593 + 3.098 x (length) + 9.247 x (weight) - 4.330 x (age). The Nelson equation, including not only LBM but FM as additional predictor, was the best predicting equation ([108 LBM + 16.9 FM]0.239). Harris-Benedict equation had sufficient precision also in extreme obese subjects with a body weight > or = 120 kg, so there is no need for adaptation.