Standardizing Terminology for Estimating the Diet-Dependent Net Acid Load to the Metabolic System

Abstract

Contemporary Western diets contain acid precursors in excess of base precursors, yielding a daily systemic net acid load of varying amounts, depending on the specific composition of the diet. Increasing evidence suggests that differences in daily net acid load, resulting predominantly from differences in dietary intake, can have deleterious health consequences, with a stepwise increase in severity with increasing magnitude of the net acid load. The daily net acid load’s magnitude (in part by influencing systemic acid–base status) has been shown to induce renal losses of calcium, magnesium, and nitrogen and adversely affects numerous endocrine functions. Investigations have shown detrimental clinical outcome effects for axial and peripheral bone health, particularly in elderly subjects (1) and postmenopausal women (2), as well as healthy children (3,4). Although physiological and biochemical principles support negative effects on bone architecture, muscle wasting, and nephrolithiasis, quantifying clinical outcomes is not straightforward. The long latency period required for subclinical changes to be clinically relevant and the lack of precision of current technology have posed challenges for researchers. For example, dual energy X-ray absorptiometry does not detect moderate changes in architectural-related bone strength parameters thus requiring long-term follow-up or large sample sizes. Additionally, terminological confusions result from investigators’ use of different algorithms for estimating the diet’s daily net acid load, even when the estimates derive essentially from the same input variables. For this reason, a number of plenary speakers at the 2nd International Acid-Base Symposium held in Munich, (8–9 September 2006) tried to reach agreement on terminology related to estimating the diet’s daily net acid load from the composition of the diet, based on accepted physiological principles. The group discussions yielded the following: under ordinary physiological conditions, differences in the amount of net acid produced by the metabolic system per day, which is referred to as the daily net endogenous acid production (NEAP), results predominantly from differences in the relative amounts of the diet’s acid and base precursors absorbed by the gut. Although investigators have devised several algorithms for estimating NEAP from the composition of the diet (see below), the group agreed to refer to the estimated diet-dependent net acid load as ‘‘estimated NEAP’’ and to always specify the algorithm used to obtain the estimated NEAP. For example, Frassetto et al. (5) estimated the diet’s net acid load from the diet’s contents of protein (an acid precursor) and potassium (an index of base precursors from organic anions). They would then specify: