In the process, we have seen that the human organism is able to adapt to the type of energy source it is provided with in order to survive: if a predominantly carbohydrate diet is observed, then the cells will prefer to metabolise glucose in order to derive the energy they need; conversely, a low-carbohydrate diet will lead the organism to adapt to the use of fats to satisfy its energy needs. Well, there is a way to know which energy source the body is more oriented towards. The method is based on the concept of the respiratory quotient. More specifically, regardless of which nutrient the body mainly uses, an oxidation reaction must take place to produce energy. This process involves the utilisation of some oxygen molecules and the synthesis of carbon dioxide molecules. The respiratory quotient is defined as the ratio between the number of reactant oxygen molecules and the number of carbon dioxide molecules obtained from oxidation. Well, this ratio differs depending on whether glucose or a lipid is being oxidised. The respiratory quotient is 1 in the case of predominantly glucose utilisation, while it fluctuates around the value of 0.7 (varying depending on the lipid used) in the case of predominantly lipid utilisation. The closer the respiratory quotient approaches 1, and moves away from 0.7, the greater the proportion of glucose to lipid that the body uses for metabolism. Only occasionally, in the case of diets excessively rich in carbohydrates, can the respiratory quotient take values above 1. It is possible to measure the respiratory quotient by means of a special instrument called a metabolimeter or respiratory gas analyser, which, equipped with a mouthpiece, detects the gases that are inhaled and those that are exhaled during normal lung respiration and, thus, understand the metabolic tendencies of one’s body.