What method estimates energy expenditure by measuring CO2 production and O2 consumption?

The correct choice is based on the understanding that indirect calorimetry is a widely used method for estimating energy expenditure by measuring respiratory gas exchange. This technique involves measuring the amount of oxygen consumed (O2) and carbon dioxide produced (CO2) by the body during a specific period.

Indirect calorimetry operates under the principle that the amount of energy expended can be estimated from these gas exchanges, as the oxidative breakdown of macronutrients generates CO2 while consuming O2. The respiratory quotient (RQ), which is the ratio of CO2 produced to O2 consumed, provides insights into the substrates being utilized for energy, such as carbohydrates or fats. This approach is particularly valuable in clinical and research settings for assessing metabolic rates in various populations, including those with obesity or metabolic disorders.

In contrast, direct calorimetry measures energy expenditure by assessing heat production in a controlled environment, providing a total measure of energy expenditure but without the detailed substrate utilization analysis that indirect calorimetry offers. The basal metabolic rate test focuses specifically on measuring the energy expenditure at rest, and thermogenic analysis typically involves evaluating the body's heat production related to food intake or exercise but is not specific to the measurement of respiratory gases.