The effects of diet and stool composition on the net external acid balance of normal subjects.

reported an experimental technique that permitted independent measurement of the net production of fixed endogenous acid. When compared with the simultaneous rate of renal acid excretion, external acid balance could be calculated. This technique depended upon the use of a liquid formula diet pre-pared so that it contained no potential sources of alkali. The only possible sources of fixed acid production in subjects eating the diet were from the oxidation of organic sulfur in the diet to in-organic sulfate and from the urinary losses of organic acid anions generated as free organic acids during the combustion of neutral foodstuffs. Hence, production of fixed endogenous acid could be measured as the sum of urinary inorganic sul-fate and organic acid salts. Although this diet greatly simplified the meas-urement of endogenous production of fixed acid, its limited palatability and low calcium content were unsuitable for the prolonged studies that we wished to carry out to examine the relationship between acid balance and calcium balance. The present studies were undertaken to see if a more general approach to the measurement of endogenous acid production could be devised that would be applicable to whole food diets. Three different types of diets were used, two consisting of whole foods and one a new liquid formula diet, each of which contained different amounts of po-* Submitted for publication April 11, 1966; accepted