Amino Acid Medical Foods Provide a High Dietary Acid Load and Increase Urinary Excretion of Renal Net Acid,Calcium,and Magnesium Compared with Glycomacropeptide Medical Foods in Phenylketonuria

Background. skeletal fragility is a complication of phenylketonuria (pku). a diet containing amino acids compared with glycomacropeptide reduces bone size and strength in mice. objective. we tested the hypothesis that amino acid medical foods (aa-mf) provide a high dietary acid load,subsequently increasing urinary excretion of renal net acid,calcium,and magnesium,compared to glycomacropeptide medical foods (gmp-mf). design. in a crossover design,8 participants with pku (16-35 y) provided food records and 24-hr urine samples after consuming a low-phe diet in combination with aa-mf and gmp-mf for 1-3 wks. we calculated potential renal acid load (pral) of aa-mf and gmp-mf and determined bone mineral density (bmd) measurements using dual x-ray absorptiometry. results. aa-mf provided 1.5-2.5-fold higher pral and resulted in 3-fold greater renal net acid excretion compared to gmp-mf (p=0.002). dietary protein,calcium,and magnesium intake were similar. gmp-mf significantly reduced urinary excretion of calcium by 40% (p=0.012) and magnesium by 30% (p=0.029). two participants had low bmd-for-age and trabecular bone scores,indicating microarchitectural degradation. urinary calcium with aa-mf negatively correlated with l1-l4 bmd. conclusion. compared to gmp-mf,aa-mf increase dietary acid load,subsequently increasing urinary calcium and magnesium excretion,and likely contributing to skeletal fragility in pku. © 2017 bridget m. stroup et al.