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Nonmetabolizable Base Balance: Effect of Diet Composition on Plasma pH¹

Department of Paediatrics, Faculty of Clinical Sciences, University College London, The Rayne Institute, London WC1E 6JJ, England

The pH of the plasma is determined by the concentration and chemical properties of the acids and bases dissolved in it. Three classes of acids and bases can be identified: 1) carbonic acid (CA), formed by intermediary metabolism and disposed of principally by pulmonary ventilation—variation in the rate of pulmonary ventilation controls the plasma concentration of CA; 2) metabolizable acids (MA) are either absorbed from the diet or arise in the process of intermediary metabolism and are mainly disposed of by intermediary metabolism; 3) nonmetabolizable acids and bases (NB) are absorbed from the diet and are disposed of by renal mechanisms, which also control their concentration in the plasma. Growing infants and children are in positive balance for NB, and about 96% of it is laid down in the skeleton. Because of their dietary origin and disposal in the urine, it is possible to measure the balance of nonmetabolizable acids and bases using conventional metabolic balance techniques. This is particularly important for the development of diets for young infants, as their renal mechanisms for the control of the concentration of plasma nonmetabolizable acids and bases are immature and easily overcharged. The lack of published data, however, makes it impossible to recommend maximum and minimum intakes of nonmetabolizable base.

KEY WORDS: • acidosis • acid-base equilibrium • acid-base imbalance • diet • diet therapy • milk • infant nutrition • infant • preterm • low birthweight • full-term • infant formulas

¹ This paper was presented at a symposium, "Upper Limits of Nutrients in Infant Formulas," November 7–8, 1988, In Iowa City, IA.