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Metabolism can be understood as the conversion by the human body between  food and 
accumulated fat into energy. The energy is used by the body to maintain constant 
temperature , to move and to make all the organ function. Measure of metabolism is: 
calories (cal). 

The total metabolic rate are the total  calories that the human body needs in order to 
actuate the daily functional activities. 

Resting Metabolic Rate represents the calories that the vital organs need to properly 
operate at rest ( heart , brain , lungs , liver , kidneys etc.) . RMR represents between 60 
% and 75 % of the human ‘s total metabolism. 

A knowledge of the RMR is very helpful in order to understand the nutritional needs 
and to properly manage it. 

Energy expenditure can be measured directly by putting a person in a calorimeter and 
measuring the amount of heat produced by the body mass. 

This is expensive and very impractical in the clinical setting. Energy expenditure can be 
measured indirectly with a metabolic cart by analysis of respired gases (usually expired) 
to derive volume of air passing through the lungs, the amount of oxygen extracted from 
it (i.e., oxygen uptake VO

2

) and the amount of carbon dioxide, as a by-product of 

metabolism, expelled to atmosphere (CO

2

 output  – VCO

2

). With these measurements 

the resting energy expenditure (RMR) and respiratory quotient (RQ) can be calculated.  

The RQ represents the ratio of carbon dioxide exhaled to the amount of oxygen 
consumed by the individual. RQ is useful in interpreting the results of the RMR. The 
abbreviated Weir equation is probably the most common calculation of RMR. 
Abbreviated Weir equation: 
RMR = [3.9 (VO2) + 1.1 (VCO2)] 1.44 

For best results, when having a REE done, there are certain conditions that need to be 
controlled and others that just require documenting at the time of the test. During the 
test the individual is interfaced with a  metabolic measurement system by means of a 
facemask. 

A mouthpiece with a nose clip is also sometimes used, but it may create overly stressful 
conditions to a subject (patient). 

Important considerations or conditions to improve the RMR measurement: 

• 

No food for at least 12 hours and no smoke for at least 2 hours before the test. 

• 

Maintain quiet surroundings when the test is in progress and normal temperature. 
The individual should not move arms or legs during the test.  

• 

Medications taken should be noted, such as stimulants or depressants. 

• 

The first 5 minutes of acquisition should be discarded by the computation of RMR 

• 

Steady state should be achieved, which would be identified clinically by the 
following criteria: 5 minute period when average minute VO

2

 and VCO

2

 changes 

by less than 10%, average RQ changes by less than 5% 

• 

Stable interpretable measurements should be obtained in a 15 to 20 minute test. 

• 

Renal failure patients requiring hemodialysis should not be tested during dialysis 
therapy.