Phenylketonuric diet negatively impacts on butyrate production

Phenylalanine (Phe) restricted diet, combined with Phe-free l-amino acid supplementation, is the mainstay of treatment for phenylketonuria (PKU). Being the diet a key factor modulating gut microbiota composition, the aim of the present paper was to compare dietary intakes, gut microbiota biodiversity and short chain fatty acids (SCFAs) production in children with PKU, on low-Phe diet, and in children with mild hyperphenylalaninemia (MHP), on unrestricted diet.

We enrolled 21 PKU and 21 MHP children matched for gender, age and body mass index z-score. Dietary intakes, including glycemic index (GI) and glycemic load (GL), and fecal microbiota analyses, by means of denaturing gradient gel electrophoresis (DGGE) and Real-time PCR were assessed. Fecal SCFAs were quantified by gas chromatographic analysis.

We observed an increased carbohydrate (% of total energy), fiber and vegetables intakes (g/day) in PKU compared with MHP children (p = 0.047), as well a higher daily GI and GL (maximum p < 0.001). Compared with MHP, PKU showed a lower degree of microbial diversity and a decrease in fecal butyrate content (p = 0.02). Accordingly, two of the most abundant butyrate-producing genera, Faecalibacterium spp. and Roseburia spp., were found significantly depleted in PKU children (p = 0.02 and p = 0.03, respectively).

The low-Phe diet, characterized by a higher carbohydrate intake, increases GI and GL, resulting in a different quality of substrates for microbial fermentation. Further analyses, thoroughly evaluating microbial species altered by PKU diet are needed to better investigate gut microbiota in PKU children and to eventually pave the way for pre/probiotic supplementations.