Respiratory Exchange Ratio

The respiratory exchange ratio (RER) is the ratio of metabolic carbon dioxide (CO2) production to oxygen intake O2.

Exhaled gases are compared to room air to calculate the ratio. This ratio can be used to calculate the respiratory quotient (RQ), which indicates which fuel (carbohydrate or fat) is being digested to provide energy to the body. RER is only accurate for estimating RQ during rest and mild to moderate aerobic activity without lactate buildup. The bicarbonate buffer system, among other things, contributes to the loss of accuracy during more intensive anaerobic activity. By expelling more CO2 through the respiratory system, the body attempts to compensate for the accumulation of lactate and reduce blood acidity.

Respiratory Exchange Ratio

The Respiratory Exchange Ratio (RER) is the proportion of CO2 produced by the body to the quantity of O2 consumed by the body. The respiratory quotient is the name given to this measurement when it is calculated at the cellular level (RQ). In most circumstances, measurements of the air being inhaled are used to determine it. The RER can be used to calculate total energy expenditure and assess the proportion of lipids and carbs to energy production.

A RER number approaching 0.7 indicates that fat is the primary fuel source, a value  of 1.0 indicates that carbohydrate is the primary fuel source, and a value between 0.7 and 1.0 shows that both fat and carbohydrate are used. A RER of roughly 0.8 is associated with a diversified diet. During severe exercise, the RER might potentially exceed 1.0. A value greater than 1.0.can’t be attributed to substrate metabolism, but rather to the aforementioned bicarbonate buffering effects.

Respiratory Exchange Ratio versus RQ

The respiratory quotient is the ratio of O2 to CO2exchange at the cellular level (RQ). Because it is difficult to detect RQ at the cellular level, an indirect assessment is made by measuring the gas exchange ratio of a person’s breath, also known as the respiratory exchange ratio (RER). Because the RER is an estimation of the RQ, the terms RER and RQ are sometimes used interchangeably.

How to Calculate RER

By dividing the volume of CO2produced by the volume of O2consumed, the RER is determined. At rest or during exercise, indirect calorimetry with a spirometer (or another device to monitor airflow or breath volume) and oxygen and carbon dioxide analyzers is used.

RER = volume of CO2 removed from the body/volume of O2 consumed

RER = VCO2VO2

Oxidation of a molecule of Carbohydrate:

6 O2+C6H12O6→6CO2+6H2O+38ATP

RER=VCO2VO2=6CO26O2=1.0

What do the numbers mean

RER values typically range from 0.7 to 1.0, with a low value (0.7) indicating fat burning and a high value (1.0) indicating carbohydrate burning, and numbers in between indicating a mix of fuels.

RER values are determined by the substrate used, or which macronutrients are metabolized, which is determined by the composition of food consumed by an individual. Most people who eat a balanced diet of carbs, protein, and lipids have a resting RER of 0.82. An RQ of 1.0 indicates complete glucose oxidation, which will occur during high-intensity exercise. When fasting, a score of 0.7 indicates   100% fatty acid oxidation (the value varies between 0.69 and 0.73 depending on the carbon chain length of the oxidation fatty acid). Due to the intricacy of the many methods in which different amino acids might be metabolized, no one RQ can be attributed to protein oxidation in the diet.

Energy balance and if body mass is changing, circulating insulin, and insulin sensitivity are some of the additional factors that may impact the respiratory quotient.

Respiratory Quotient

The respiratory quotient (RQ) indicates the relative contributions of fat, carbohydrate, and protein to the oxidation fuel mixture and is defined as the ratio of carbon dioxide production to oxygen consumption.

RER measurement 

Respiratory Exchange Ratio (RER)

This useful value can be used to figure out what an animal’s principal fuel source is. A particular amount of oxygen is required for the oxidation of a single molecule of glucose, and an equal amount of carbon dioxide is produced. As a result, if an animal is solely reliant on glucose for energy, its RER will be 1.

Conclusion

The respiratory exchange ratio (RER) is the proportion of metabolic (CO2) production to oxygen intake  (O2).

The ratio is calculated by comparing exhaled gases to room air. The respiratory quotient (RQ) can be calculated using this ratio, which reveals which fuel (carbohydrate or fat) is being digested to deliver energy to the body. RER is only useful for assessing RQ during rest and light to moderate aerobic activity that does not result in lactate accumulation.

At the cellular level, the respiratory quotient is the ratio of O2 to CO2 exchange (RQ). Because detecting RQ at the cellular level is challenging, an indirect assessment is achieved by measuring a person gas exchange ratio, also known as the respiratory exchange ratio (RER).

The substrate used, or which macronutrients are metabolized, which is decided by the composition of food consumed by an individual, determines RER levels.