History of nutrition and acid-base physiology.

In the 17th century the notion of nutrition and diet changed in northern European countries. First chemical experiments fostered the idea that salts resulted from a union of acids and bases. Digestion was no more regarded as a process of cooking but a succession of fermentations controlled by a balanced production of acids and alkali. Life seemed to depend on the equilibrium of acids and alkalis. In the 19th century food was systematically analysed for the content of energy and macronutrients and first scientifically based nutritional standards were formulated. The preferred use of processed food from the new food industry resulted in epidemics of nutritional disorders. Acidosis seemed to be a plausible pathogenic factor. Practitioners (S Ishizuka, H Hay, FX Mayr) formulated holistic doctrines integrating the concept of balance of acids and bases and recommending food with an excess of alkali. New micromethods to determine the concentration of electrolytes and blood acid-base status promoted physiological and clinical research into acid-base metabolism in the 1960s. In the new physiologically based terminology of systemic acid-base status, the relationship between blood acid-base status and net acid intake or excretion was, however, incorrectly simplified. In the 1970s metabolic acidosis was observed in patients on chemically defined diets and parenteral nutrition. Based on the data of comprehensive acid-base balance studies, calculation models were used to estimate renal net acid excretion from nutrient intake and to predict the potential renal acid load of single foods. Extrapolating current trends to the future, one can say that acid-base physiology will probably remain a challenge in nutrition and functional medicine over the next few years. The challenge will include new concepts for the manipulation of nutritional acid load in sports, dietetics and preventive medicine as well as new definitions of the upper intake level of potential renal acid load in functional foods and the monitoring of renal net acid excretion in populations.