Explain the term Indirect Calorimetry?

This method estimates energy expenditure by determining the oxygen consumption and carbon dioxide production of the body or a cell over a given period of time. Data so obtained from this method permits calculation of the respiratory quotient (RQ) which is expressed as:

RQ = moles CO₂ expired / moles O₂ Consumed

The RQ indicates the source of metabolic energy. It ranges from 1.0 (carbohydrate oxidation) to 0.7 (fat oxidation). On a mixed diet the RQ is about 0.85. This determination is converted into kilocalories of heat produced per square meter of body surface area per hour and is extrapolated to energy expenditure in 24 hours.