Nutritional Practices and Knowledge of Patients with Phenylketonuria

<b>Background/Objectives</b>: Phenylketonuria (PKU) is an inborn error of metabolism (IEM) that requires a specialized medical nutrition therapy (MNT) to maintain blood phenylalanine concentrations within a safe range. This study aimed to assess nutrition practices, knowledge, and PKU diet adherence in patients with PKU. <b>Methods</b>: This cross-sectional study included 27 patients (<i>n</i> = 19 women) with PKU, recruited from clinics of IEM in Greece, ranging in age between 14 and 60 years, with PKU diagnosis via neonatal screening. Each participant completed the questionnaire independently. For the two patients with age below 18 years old, caregivers provided written informed consent. All participants were questioned regarding their dietary practices, nutritional knowledge, and perceptions. <b>Results</b>: More than half (66.7%) of patients complied with the PKU diet and the recommended daily protein substitutes. However, 25.9% reported being unaware of their blood phenylalanine levels, and 40.7% didn't know how many PKU exchanges they consumed daily. Most patients (88.8%) perceived the recommended PKU diet as "healthy", and reported feeling well when adhering to it. Several concerns were raised regarding protein substitutes, with 10.5% of patients feeling that the amount of prescribed protein substitutes was too high, while 25.9% perceived it as being too low. Additionally, 14.8% of patients expressed concerns regarding the protein amount required for building muscle mass. Overall, the majority of participants perceived the PKU diet as being adequate in energy, carbohydrates, lipids, and protein. <b>Conclusions</b>: Although patients with PKU generally possess a good understanding of PKU nutritional principles, significant potential for improvement in dietary education is apparent. To support optimal management of blood phenylalanine concentrations, it is essential to implement novel communication strategies that facilitate patient adherence to the MNT for PKU. Such strategies should also empower caregivers to provide effective support, including the proper use of protein substitutes and accurate protein exchanges.