Simplifying the diet for patients with phenylketonuria (PKU): unrestricted consumption of fruit and vegetables

Peer-reviewed | Manuscript received: June 23, 2014 | Revision accepted: September 09, 2014

Introduction

Phenylketonuria (PKU) (OMIM¹ 261600) is one of the most common congenital metabolic disorders. The phenylalanine (Phe) hydroxylase enzyme needed to break down phenylalanine exhibits significantly reduced activity as a result of mutations in the encoding gene. Untreated, it causes severe psychomotor retardation. Only thanks to early diagnosis as part of newborn screening and immediate commencement of treatment by means of a strict, protein-restricted diet will patients develop normally [1, 2].

Dietary treatment is based on the principle of substrate reduction (Phe) and product supplementation (tyrosine, other amino acids, micronutrients). Metabolic control is monitored by regular determination of the Phe concentration in plasma or dried blood. Depending on the residual activity of phenylalanine hydroxylase, each PKU patient has an individual Phe tolerance level. This is the amount of Phe, which can be introduced with food, without Phe plasma concentrations exceeding the therapeutic range. In patients with classical PKU, the average Phe tolerance is only approx. 200–400 mg/day, which corresponds to approx. 5–10 g protein/day.

Summary

Over a period of three years, the phenylalanine content in fruit and vegetables was not taken into account in the daily phenylalanine balance for patients with phenylketonuria, a congenital metabolic disorder. In spite of a significantly higher intake of phenylalanine, no worsening of metabolic control could be detected.

Keywords: phenylketonuria, phenylalanine, metabolic disorder, diet, balancing, fruit consumption, vegetable consumption

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