Relationship of Renal “Net Acid” Excretion to Titratable Ash-Acidity (Ash-TA) in Diet and Feces. ∗

Summary

Titratable ash-acidity (ash-TA) has been described as an acid-base parameter which is based solely on mineral composition and may therefore be defined strictly in terms of biologically stable chemical elements. Renal “net acid” values were shown to consist of two components: 1) the urinary ash-TA value, which varies markedly with diet composition and remains generally equal to the value for net absorption of dietary ash-TA, and 2) a relatively small and essentially constant quantity equal to the urinary organic anions value minus the values for urinary organic sulfur, organic phosphorus and organic cations. Most of the second component was accounted for by the organic anions value, so that the renal “net acid” values were generally slightly higher than the corresponding urinary ash-TA values. The renal “net acid” values nevertheless remained closely correlated with the corresponding urinary ash-TA values and hence with the values for net absorption of dietary ash-TA. No basis was found for relating either ash-TA intake or excretion to true endogenous acid production; however, it was shown that both ash-TA values and renal “net acid” values correspond theoretically to approximate evaluations of “potential” acid.