Why Measure RMR Rather than Use Predictive Formulas?

The Resting Metabolic Rate (RMR) is the rate at which the body burns energy when it is at complete rest. It indicates the number of calories the body needs to perform basic functions like breathing and circulation. The RMR is part of the individual's total daily energy expenditure (TDEE) or the total number of calories the body burns each day.

The term basal metabolic rate (BMR) is often confused and/or interchanged with RMR or resting energy expenditure (REE). However, BMR measurements must meet total physiological equilibrium whereas RMR conditions of measurement can be altered and defined by the contextual limitations. Therefore, BMR is measured in the elusive "perfect" steady state, whereas RMR measurement is more accessible and more commonly used. 

 

Predictive formulas have long been used to "measure" the RMR because an actual measurement through Indirect Calorimetry has not been practical. But the truth is, while predictions might hold their ground statistically, when applied to individuals, they are woefully inadequate. In an examination of published articles examining the validity of various predictive equations, Frankenfield, Roth-Yousey and Compher found that even the best equation (Miffin-St Jeor) was only within 10% of measured results. While 10% may seem statistically acceptable, for the individual desiring to lose weight, an RMR estimate that is 10% higher (2200 kCals) than an actual measurement of 2000 kCals a day would be significant. That additional caloric intake would result in 21 pounds gained in one year. Additionally, these same researchers noted that errors and limitations with equations exist when applied to individuals, and that “RMR estimation errors would be eliminated by valid measurement of RMR with indirect calorimetry.” (Frankenfield D, et al, J Am Diet Assoc. 2005 May;105(5):775-89.)

 

Additional researchers at the University of Pennsylvania noted that the obese have Resting Energy Expenditures that are particularly difficult to predict. Their findings read, “Caloric prescription for weight reduction must be tailored to individuals rather than recommending the same caloric intake to persons with varying metabolic rates.” (Foster GD, et al, Metabolism. 1988 May;37(5):467-72.)