Inclusion Criteria:  The study will include subjects over the age of 18 who have PKU or hyperphenylalaninemia and are expected to have dietary treatment according to expert recommendations. A prerequisite for entering the investigation will be a signed consent to participate in the investigation and the ability of the participant to have a good understanding of the content of the research and to fully participate in the interventional dietary process.  Exclusion Criteria:  The investigators will not include adult patients who do not manage their diet on their own and need caregivers due to limited cognitive abilities (patients with late-diagnosed disease and neurological consequences of the disease) or who do not want to sign an informed consent.