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

Abstract EN

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.

The trial was registered at clinicaltrials.gov as NCT01428258.