The protein metabolism cannot be determined via a breath gas measurement, but can only be determined via a urine sample.
The protein metabolism differs only very slightly from person to person. We have therefore used an average value here.
Protein metabolism has little relevance for recommendations for health, exercise and nutrition. Carbohydrate and fat metabolism, on the other hand, is very relevant.

Explained in more detail: Measurement of metabolic substrates via the O2 and CO2 values of respiration
The analyzer has both an O2 sensor (statement about fat metabolism) and a CO2 sensor (statement about carbohydrate metabolism). The respiratory quotient, which is the ratio between the CO2 produced or exhaled and the O2 value absorbed by the body, can be used to determine the individual ratio and the exact proportion of metabolic substrates in the resting situation.