Question

What’s the “respiratory quotient” and why does it vary depending upon the kinds of food used to provide energy?

What other factors affect the respiratory quotient?

On average, why is the volume of air that we breathe in slightly larger than the volume of air that we breathe out? (please explain in relation to the respiratory quotients of fats, carbs, proteins, etc.)

Answer 1

Hi Answer:

Q.1. What’s the “respiratory quotient” and why does it vary depending upon the kinds of food used to provide energy?

Answer: The respiratory quotient is commonly known as RQ. This term was first used in 1879. It is the ratio of the volume of CO₂ evolved to that of O₂ consumed by an organism, tissue or individual cell in a given time interval CO_2evolved/ O_2consumed

Application of RQ in medical science: (i)The RQ has mainly used in case of the chronic obstructive pulmonary disease under which a patient lose a large amount of energy for respiration. (ii) RQ is helpful to determine the under and overfeeding to a patient. An underfeed patient have low RQ whereas overfeed have high RQ.(iii) it can be used to analyze the liver function and the diagnosis of liver diseases.

RQ depending on food type: As we know that the RQ is the used ratio of CO₂ evolved and O₂ consumed during food metabolism. The value of RQ also varies with the food consumption. Because we know that most of the foods (fats, carbohydrates, protein etc.) items have Carbon, hydrogen, and Oxygen. The amount of these substances (C, H, O) also varies from food to food hence during metabolism the RQ values varies from 1 to 7. It can be explained like this, for example, the metabolism of carbohydrates. The glucose is oxidized into CO₂ and water as shown below:

C₆H₁₂O₆ + 6 O₂ ? 6 CO₂+ 6 H₂O, here the ratio of CO2 to O2 is equal so RQ is 1.

Whereas, it is different for fats and proteins because the chemical composition of fats & proteins is different from carbohydrates. It has less oxygen atom whereas the quantity of carbon and hydrogen atom is high.

For Fats: C₁₆H₃₂O₂ + 23 O₂ ?16CO₂ +16 H₂O., here the ratio RQ is 16CO₂ /23O₂ =0.696.

For Proteins : C₇₂H₁₁₂N₁₈O₂₂S + 77O₂ ? 63CO₂ + 38H₂O + SO₃ + 9 CO(NH₂)₂ here the ratio RQ is 63CO₂ / 77O₂ =0.8.

Hence we can say that the RQ is totally depending on the nature of food which we consume.

Q. 2. What other factors affect the respiratory quotient?

Answer: The most common factor which affects the RQ is:

Pulmonary disease such as chronic obstructive pulmonary disease. In such disease, the patient needs more oxygen and have high RQ value.

Type of food consumptions: RQ varies from food to food when we had food rich in carbohydrates which are converted into fats the RQ will also rise because oxygen-rich substance converted into oxygen-poor substances.

Acidosis: during this condition, the CO₂ output is more than O₂ consumption so RQ rises

alkalosis: during alkalosis RQ falls because respiration is depressed and CO₂ will be retained in the body

The rise in body temperature: Increase the RQ because it increases the breathing which brings more Oxygen

Diabetes: RQ falls down because of diabetes fewer carbohydrates burn and energy is supplied mainly by fat burning.

Starvation: Low RQ because the energy is derived mainly from the burning of fats

Muscular exercise: in normal exercise RQ is unchanged but in heavy exercise, RQ rises because breathing rate increases which wash out more carbon from body.

Q.3. On average, why is the volume of air that we breathe in slightly larger than the volume of air that we breathe out? (please explain in relation to the respiratory quotients of fats, carbs, proteins, etc.)

Answer: The volume of air that we breathe in slightly larger than the volume of air that we breathe out the reason behind it is the residual volume of lungs; Lungs kept some volume inside them so the volume of exhaling air is always less than the volume of inhaling air. The second reason is the change in RQ during the metabolism of different kind of food inside the body also affect the exhale volume. It can be explained like this. By taking examples of various foods such as fats, carbs, protein: In these foods, different amount of C, H, O are present which carries the oxygen consumption and CO₂ evolution.

RQ for Carbohydrates:

C₆H₁₂O₆ + 6 O₂ ? 6 CO₂+ 6 H₂O, here the ratio of CO2 to O2 is equal so RQ is 1.

In case of glucose metabolism, equal amount of carbon dioxide and an equal number of oxygen is required.

RQ for Fats:

C₁₆H₃₂O₂ + 23 O₂ ?16CO₂ +16 H₂O., here the ratio RQ is 16CO₂ /23O₂ =0.696.

In case of fats oxygen requirement is more as compared to carbon dioxide.

RQ for Proteins

C₇₂H₁₁₂N₁₈O₂₂S + 77O₂ ? 63CO₂ + 38H₂O + SO₃ + 9CO(NH₂)₂ here the ratio RQ is 63CO₂ / 77O₂ =0.8.

In case of proteins oxygen requirement in large as compared to carbon dioxide.