Most of the daily acid load is produced by which source?

• A. Dietary intake
• B. Obligatory metabolic functions
• C. Both equally
• D. None

Answer: (B)

Daily acid load comes primarily from obligatory metabolic processes. Even in the fasting state, the body continually generates fixed acids as a result of normal metabolism—oxidation of sulfur-containing amino acids (like methionine and cysteine) produces sulfuric acid, and phosphate groups from ATP and nucleotides release phosphoric acid. These acids must be buffered and then eliminated by the kidneys, making up the majority of daily acid production. Diet can influence acid-base balance, but the amount of acid arising from metabolism far outweighs what is derived from dietary intake, so obligatory metabolic functions are the main source of daily acid load.