Techniques to Study Metabolism

Metabolism represents the “ensemble” of biochemical reactions, ensuring proper cell homeostasis and correct body functioning. The redox reactions of chemical species lead to energy transformation and heat production. Different strategies have been developed over the time to measure the energy consumed by the body to maintain its homeostasis during daily life as well as to investigate specific metabolic pathways and biochemical substrates utilization. In this chapter, a brief overview is offered on the application of the key techniques to examine human metabolism. Direct calorimetry is performed in a confined space and relies on body heat production to evaluate energy expenditure. The method is time-consuming and requires an isolated chamber specifically equipped for the purpose. Indirect calorimetry is the technique that assesses energy expenditure through measuring O2 and CO2 exchanges, which reflect body energy consumption. Indirect calorimetry allows to obtain data on substrate oxidation. Doubly labelled water is a very accurate system for measuring energy expenditure in free-living condition. It uses spectrometric measure of labelled isotopes (2H, 18O) excreted through urine and breath to estimate metabolic rate. Accelerometers are devices that estimate energy expenditure by computing body movements with accessory biological measures. Their accuracy is still debated, especially in obese subjects. Finally, RM spectrometry is a technique employed to explore biochemical pathways and metabolic fate of energy substrates.