What methods measure energy expenditure?

Methods for measuring energy expenditure include:

1. Doubly Labeled Water:

   • This method involves tracking the elimination of isotopes in the urine after they have been ingested with water. It provides an estimation of energy expended over a longer period, usually several weeks.

2. Indirect Calorimetry:

   • This method measures the oxygen consumption (O2) and carbon dioxide production (CO2) during rest or activity. It's frequently used in exercise testing and can determine the respiratory quotient (RQ), which relates these gases to the type of fuel (fat or glucose) being used by the body.

3. Metabolic Chambers:

   • These highly controlled environments measure total energy expenditure by tracking the amount of oxygen consumed and CO2 produced in an enclosed setting, typically over 24 to 48 hours.

Each of these methods provides insights into different aspects of metabolic rate and can elucidate how calories are being used within the body, whether from fats, proteins, or carbohydrates 1.