Question

What is meant by respiratory quotient (RQ)? When will the value of RQ be $1$ and when will it be less than $1$?

Answer 1

Respiration is a process where inhalation of oxygen and exhalation of carbon dioxide take place. The respiratory quotient, often known as the respiratory ratio (RQ), is the ratio of carbon dioxide exhaled to oxygen consumed during breathing. RQ is used for analysing the proper functioning of the body.

Complete answer:
During respiration in the human body, oxygen is consumed and carbon dioxide is released. The respiratory quotient is defined as the ratio of carbon dioxide emitted to oxygen consumed during cellular respiration. RQ is the abbreviation for the term.
Respiratory quotient is given by the formula, RQ= Volume of carbon dioxide eliminated/ Volume of oxygen consumed
The value of respiratory quotient indicates which macronutrients are being metabolized in the body, as different energy pathways are used for fats, carbohydrates and proteins. The RQ value ranges from $1.0 - 0.7$.
RQ of 1 denotes that carbohydrates are metabolized in the body. It means that carbohydrates are being used as a substrate and getting oxidized. RQ of $1$ indicates that the individual’s diet is primarily containing carbohydrates.
RQ less than $1$ denotes those fats and proteins that are being metabolized in the body. RQ of $0.7$ denotes fat oxidation. RQ of $0.8 - 0.9$ denotes protein oxidation.

Note:
RQ is measured using Ganong respirometer. The RQ for a mixed diet containing fat, protein and carbohydrates in equal proportions will be $0.8$. The calculation of RQ is used for many applications. It is used as an indicator of over or underfeeding, used for analysing the functioning of the liver, useful in diagnosing liver cirrhosis, pulmonary diseases etc.