Effect of diet on plasma acid-base composition in normal humans

Abstract

Steady-state plasma and urine acid-base composition was assessed in 19 studies of 16 normal subjects who ingested constant amounts of one of three diets that resulted in different rates of endogenous noncarbonic acid production (EAP) within the normal range. Renal net acid excretion (NAE) was used to quantify EAP since the two variables are positively correlated in normal subjects. A significant positive correlation was observed between plasma [H+] and plasma P(CO2,) and between plasma [HCO3-] and plasma P(CO2,) among the subjects. Multiple correlation analysis revealed a significant interrelationship among plasma [H+], plasma P(CO2), and NAE (r = 0.71, P < 0.001). The partial correlation coefficients indicated a significant positive correlation between plasma [H+] and NAE, and a significant negative correlation between plasma [HCO3-] and NAE, when plasma P(CO2) was held constant. These findings indicate that two factors influence the level at which plasma [H+] is maintained in normal subjects: (1) the steady-state rate of endogenous noncarbonic acid production, and (2) the set-point at which plasma P(CO2) is regulated by the respiratory system. Plasma [HCO3-] is also co-determined by these two factors. In disease states, therefore, both factors must be known before a disturbance in acid-base homeostasis can be excluded.