Calculation of Energy Expenditure from RQ

•Once the RQ has been computed from gaseous exchange, the calculation of energy expended is rather simple. Table below gives the caloric value for 1 L of O2 and for 1 L of CO2 given various RQs.

•When the amount of O2 and/or CO2 in the exchange has been determined, the total caloric value represented by the exchange can be calculated. It is also possible to determine the amount of carbohydrate and fat being oxidized in the production of these calories.

•For example, if under standard conditions for the determination of BMR a person consumed 15.7 L O2/hr and expired 12.0 L CO2, the RQ would be 12.0/15.7 = 0.7643.

•From Table, the caloric equivalent for an RQ of 0.76 is 4.751 for 1 L O2 or 6.253 for 1 L CO2. Based on the caloric equivalent for O2, calories produced/hr are 15.7 x 4.751 = 74.59. Based on the caloric equivalent for CO2, calories produced/hr are 12.0 x 6.253 = 75.04.

•If we then use 75 kcal/hr as the caloric expenditure, then under basal conditions the BMR for the day would be approx. 1,800 kcal (75 kcal/h x 24). At this RQ of 0.76, fat is supplying almost 81% of energy expended (Table).    

•Because under ordinary circumstances the contribution of protein to energy metabolism is so small, the oxidation of protein is ignored in the determination of the so-called nonprotein RQ.