Potential Renal Acid Load of Foods and its Influence on Urine pH
Section snippets
Calculation Model
The method used for calculation of the PRAL of foods is based on the calculation model we developed for prediction of NAE from nutrient intake data (4). The directly determined NAE (based on urine analyses) is calculated in the conventional manner as the sum of titratable acid and ammonium minus bicarbonate (Fig. 1). As is discernible from Fig. 1, NAE can also be determined indirectly from the difference of the sum of the remaining important urinary anions — chloride, phosphorus, sulfate, and
Results
The calculated acid-forming potential (or base-forming potential) of more than 100 frequently consumed foods and beverages is listed along with postabsorptive urinary determinants, sulfate, phosphorus excess, and alkali excess, according to nine main food groups in Table 2. The calculation model yielded PRAL values ranging from a maximum of 34.2 mEq/100 g (parmesan cheese) over 0 mEq/100 g for fat and oils to a minimum of −21 mEq/100 g (raisins). Among the raw (ie, nondried) fruits, the
Discussion
According to the calculation model described, negative PRAL values (indicating an excess of the base-forming potential of foods) were nearly exclusively found in the vegetable and fruit groups. In contrast, the highest acid loads originated in cheese, followed by meat, fish, and grain products. Similar trends, although with marked deviations for individual foods, were observed by other investigators whose calculations were based on acid-alkaline ash analyses (13), (14) or on current food tables
Implications and Applications
A formula for the prediction of urine pH using nutrient intake data has been developed for cats (15), a species with a high incidence of struvite stones. To our knowledge no such prognostic method has been available hitherto for human beings consuming normal mixed diets. Based on PRAL values presented herein, which consider mean intestinal absorption rates for individual nutrients and postabsorptive metabolism of sulfur-containing amino acids, it is possible to estimate the diet-dependent
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