Peter Attia· MD
indirect calorimetry is really classical physics if you will in which the rate of oxygen consumption and the rate of carbon dioxide are measured in a number of ways the most frequent is to put a mask or hood over the head of the individual and whom the measurement is made and simply use gas sensors and flow meters to quantify the amount of oxygen consumed and co2 released and from that information one can quite easily calculate how many kcals of energy are being expended to correlate if you will to account for the amount of oxygen consumed in the co2 produced and by looking at the ratio of those two one can even get a indication of the kind of fuel that's being burned