The purpose of breathing is to bring oxygen into the body and to rid the body of waste gases such as carbon dioxide and excess water vapor. This is done by diffusion with the blood. I am wondering whether the respiratory system also "accidentally" removes good gases from the body via diffusion and exhalation. (These good gases do not include oxygen, since it doesn't diffuse from the blood into the lungs.) This might be useful if a person has low amounts of a good gas and breathing too much, such as doing too much exercise, is the culprit.
Such good gases could come from food. Just like alcohol vapor is exhaled, maybe these gases might be exhaled too. Good gases could also come from a specific metabolic process.