Met Acid Balance in Growing Infants

Abstract

Methods recently developed by KILDEBERG et al. [ACta paed. scand. 58: 321, 1969] permit the quantitation of net acid balance (NAB) in growing infants for the first time. NAB consists of the difference between net acid intake (NAI) and urinary net acid excretion (NAE). NAI, defined as the daily net gain of non-carbonic, non-metabolizable acid from all extrarenal sources, consists of contributions from G-I absorption, sulfuric acid production, organic anion (OA-) excretion, skeletal mineralization (Ca++ balance) and soft tissue growth, each of which can be measured or approximated. Daily NAB was determined in 3 groups of 6 to 12 growing healthy permature infants fed 100–120 Cal/kg/d of either PM60/40^R (group A, 50 periods), Similac^R (group B, 28 periods), or a standard cows milk formula (group C, 28 Periods). All formulae contained surprisingly large loads of undertermined anion [UA = (Na⁺+ Ca⁺⁺+ Mg⁺⁺) − (Cl⁻+1.8P)], being lowest in A and highest in C, but since fecal UA approximated oral intake of UA in all groups, net absorbed UA (potential base) was small. Sulfuric acid production was low in A and B and higher in C. Acid load due to urinary OA- excrection was significant and similar in all groups, while that due to skeletal growth was proportional to Ca⁺⁺ intake. Despite differences in the amount and pattern of NAI,NAE closely matched NAI so that NAB was not different from zero in any group. These results show that normal growth is accompanied by a relatively high level of acid production, the pattern and amount of which can be altered in response to type of dietary intake. They also suggest a heretofore unrecognized role of the G-I tract in defense against potential base load of commonly used formulae.

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