Recognizing this limitation, Remer and Manz developed food-rating values that they refer to as PRAL (potential renal acid load) and the NAE (net acid excretion).(1) The NAE can be determined directly by measuring the acid and the ammonium appearing in the urine and then subtracting out the measured urinary bicarbonate. This method yields a net acid excretion score based on direct measurements of the urine. This score, however, reflects total acid and base load of a mixed diet and not the acid or base load of the individual foods in the diet.

To more accurately predict the acid or base potential of a given food, another technique is needed. Unlike the aforementioned technique, the NAE can be determined indirectly by adding up all the urinary acidic anions from the above method and subtracting out the basic/alkaline cations described above. Since the urinary anion and cation excretion is directly related to food intake, it's possible to approximate net acid or base load from the composition of the food. This net acid or base load is called the PRAL (potential renal acid load).

Therefore, in taking into account the composition of the food, the bioavailability of the different micro and macronutrients (especially protein) of the food, the sulfur content of the food, and the obligatory diet-independent organic acid losses, it's then possible to estimate a physiologically meaningful index of the acid or base load based on the food consumed (PRAL).

For those of you who don't really care about PRALs and NAEs, here's the one sentence summary of what I'm talking about. In layman's terms, researchers can now analyze a food and based on its components, determine what the true acid or base load on the body will be. If you're still wondering why this is important, read on.