Denise Ney, PhD

Slide of the Week: Denise Ney, PhD

Title: 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.

Legend: Potential renal acid load (PRAL) was calculated for 10 types of amino acid medical foods (AA-MFs) and three types of glycomacropeptide medical foods (GMP-MFs) to predict dietary acid load based on amino acid and mineral analysis, n = 2-3/medical food. Nine of 10 AA-MFs have a high PRAL. Renal net acid excretion (RNAE) was significantly higher with AA-MFs compared to GMP-MFs (P = 0.002), which proves that AA-MFs have a high dietary acid load. Urinary calcium excretion was significantly higher with AA-MFs compared with GMP-MFs (P = 0.012) as well.

Citation: Stroup BM, Sawin EA, Murali SG, Binkley N, Hansen KE, Ney DM. (2017). 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. Journal of Nutrition and Metabolism, 2017:1-12. doi: 10.1155/2017/1909101.

Abstract: Background. Skeletal fragility is a complication of phenylketonuria (PKU). A diet containing amino acids compared to one with glycomacropeptide reduces bone size and strength in mice. Objective. We tested the hypothesis that AA-MFs provide a high dietary acid load, subsequently increasing urinary excretion of renal net acid, calcium, and magnesium, compared to GMP-MFs. Design. In a crossover design, eight participants with PKU (16–35 y) provided food records and 24-hr urine samples after consuming a low-Phe diet in combination with AA-MFs and GMP-MFs for 1–3 weeks. We calculated PRAL of AA-MFs and GMP-MFs and measured bone mineral density (BMD) using dual X-ray absorptiometry. Results. AA-MFs provided 1.5–2.5-fold higher PRAL and resulted in 3-fold greater renal net acid excretion compared to GMP-MFs. Dietary protein, calcium and magnesium intake were similar. GMP-MFs significantly reduced urinary excretion of calcium by 40% and magnesium by 30%. Two participants had low BMD-for-age and trabecular bone scores, indicating microarchitectural degradation. Urinary calcium with AA-MFs negatively correlated with L1–L4 BMD. Conclusion. Compared to GMP-MFs, AA-MFs increase dietary acid load, subsequently increasing urinary calcium and magnesium excretion, and likely contributing to skeletal fragility in PKU. The trial was registered at as NCT01428258.

About the Lab: The Ney research group has conducted studies in individuals with PKU that establishes the acceptability and safety of foods made with the whey protein, glycomacropeptide, in the nutritional management of PKU. PKU is a genetic disorder caused by deficiency of the hepatic enzyme phenylalanine hydroxylase that converts the essential amino acid phenylalanine to tyrosine. To prevent brain damage and cognitive impairment, individuals with PKU must follow a lifelong, low-phenylalanine diet that is restricted in natural foods and requires ingestion of a bitter-tasting amino acid formula. Glycomacropeptide (GMP) is uniquely suited to the PKU diet because it is the only known dietary protein that contains only trace amounts of phenylalanine. Low-phenylalanine food products made from GMP provide a palatable and acceptable alternative to the amino acid formulas currently required in the PKU diet.

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