Thank you for this interesting question.
We recently tested 35 predictive equations in a group of 227 inpatients and 188 outpatients. In total group, Korth (2007) and FAO/WHO/UNU (1985) with weight and height and Marra (2003) were most accurate but, even in these best performing equations, only 50% of the patients the REE was calculated accurately (within +/-10% of calorimetry measurement). In BMI subgroups, FAO/WHO/UNU (1985) predicted REE accurately in 44% of underweight, 52% of normal weight and 61% of overweight patients. In obese patients, Mifflin (1990) with weight and Weijs (2008) predicted 57% accurately. Age, BMI, FFM, FM and CRP appeared to be predictive determinants in calculating REE. Building a new equation with these determinants did not improve the percentage of accurately caluculated REE.
Our conclusion is that existing predictive equations do not predict REE accurately. When indirect calorimetry is not available, FAO/WHO/UNU (1985) with weight and height is best usable in underweight, normal weight and overweight patients. In obese patients, Mifflin (1990) with weight and Weijs (2008) are best usable. Age, BMI, FFM, FM and CRP are predictive determinants but do not improve predicted REE.
These results will be presented for publication to a scientific journal soon.
Your question on additional factors to calculate TEE is topic of discussion. Since activity will be reduced during illness we use either an additional factor for activity OR for disease. In most patients an additional factor of 30% will be enough. In specific patient groups more scientific information on additional factors is available. Still, we keep the maximum of 50% to prevent accumulation of additional factors.
Dr. Peter Weijs is the expert in this field of our group. He promised to comment on this topic later next week at this forum.