Body acidity has to be kept at a fairly constant level.
Tertiary structure of most proteins dependent on the ambient pH in particular, the activities of most enzymes sensitive to the [H+]
Normal pH range within body fluids 7.32 - 7.35.
Normal pH is constantly being attacked by metabolic processes within the body that produces acidic metabolites.
The catabolism of carbohydrates generate large amounts of carbon dioxide which are excreted by the lungs.
The acidic residues from protein catabolism (example sulphur containing amino acid - cysteine), produces fixed or nonvolatile acids that are excreted by the kidneys.