Question

If you have a CO2 value of 1.7 L/min and a VO2 2.2 L/min what would the RER value be? What substrate is primarily being used and how was this determined? Please show work and steps.

Answer 1

The respiratory exchange ratio (RER) is the ratio between the amount of carbon dioxide (CO2) produced in metabolism and oxygen (O2) used.    RER = VCO2/VO2.

By knowing this value, you can determine what fuel is being used for energy production and you can calculate energy expenditure for a given activity. An RER of 0.7 indicates that fat is the predominant fuel source, a value of 1.0 is indicative of carbohydrate being the predominant fuel source, and a value between 0.7 and 1.0 suggests a mix of both fat and carbohydrate.

RER = 1.7 L/min / 2.2 L/min = 0.7.(rounding off),

Since the RER ratio  is 0.7 it means fat is the predominant source.