Respiration & Nutrition

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“How much we need oxygen to live” is only felt at the lack of it. Process of respiration is the fundamental biological process that sustains life. In the exchange of harmful CO2 ; O2 is exchanged. Further without O2 no energy liberating combustion can take.
Combustion (process of energy release) in living being was first described by Lavoisier (1743-1794). He discovered the true nature of oxygen & how it’s combustion with carbon & hydrogen result in the formation of CO2, H2O and heat.
In 1842, Liebig discovered that the substances burned in the body for energy liberation are carbohydrate, fat & protein.
Importance of respiratory exchange ratio in knowing the nutrient fuel of body:
In one breath, you normally breathe in more molecules of oxygen than you breathe out molecules of carbon dioxide. The ratio between these CO2 / %O2 is the respiratory exchange ratio (RER).
Measuring this ratio can be used for estimating the respiratory quotient (RQ), an indicator of which fuel (carbohydrate or fat) is being metabolized to supply the body with energy.
RER is about 0.8 at rest with a modern diet. This value however, can exceed 1 during intense exercise, as CO2 production by the working muscles becomes greater and more of the inhaled O2 gets used rather than being expelled. It is important to note that during exercise, using RER for estimating RQ loses accuracy because of factors including bicarbonate buffering of lactic acid, which affects the CO2 levels being expelled by the respiratory system.
Calculation of RER is commonly done in conjunction with exercise tests such as the VO2 Max Test and can be used as an indicator that the participant is nearing exhaustion and the limits of their cardio-respiratory system. An RER of approximately 1.2 is reached at this point.
An RER of 0.70 indicates that fat is the predominant fuel source, RER of 0.85 indicates a mix of 50/50 between fat and carbohydrates, and any value above 1.00 is indicative of carbohydrate being the predominant fuel source.

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