Evaluation of PKU UP

Inclusion Criteria: * Diagnosis of PKU requiring a low-protein diet and protein substitute. * Participants who are adherent with their blood phenylalanine (Phe) testing, in the opinion of the investigator. * Participants aged 1-10 years. * Participants who in the opinion of the investigator are anticipated to be able to take at least half of their daily protein equivalent requirement from PKU UP (in order to assess this, a taste test (or similar) may be conducted at investigator's discretion as part of the screening process). * Willingly given, written, informed consent from the parent(s)/guardian(s). * Willingly given, written assent by the participant (if appropriate). Exclusion Criteria: * Inability to comply with the study protocol, in the opinion of the investigator. * Any co-morbidity, which, in the opinion of the investigator, would preclude participation in the study. * Diagnosis of persistent hyperphenylalaninemia, or mild PKU not requiring a low protein diet and protein substitute. * Allergy or intolerance to milk. * Participants who are currently participating in, plan to participate in or have participated in an interventional investigational drug, food or medical device study within 30 days prior to the screening visit. * Use of additional micronutrient supplements during the evaluation period, unless clinically indicated and prescribed by the Investigator (must be recorded in both the medical records and case report form).