Nutritional Consequences of Adhering to a Low Phenylalanine Diet for Late-Treated Adults with PKU

Background: The main treatment for phenylketonuria (PKU) is a low phenylalanine (Phe) diet, phenylalanine-free protein substitute and low-protein special foods. This study describes dietary composition and nutritional status in late-diagnosed adult patients adhering to a PKU diet. Methods: Nineteen patients, followed at Oslo University Hospital in Norway, participated; median age was 48 years (range 26–66). Subjects were mild to severely mentally retarded. Food intake, clinical data and blood analyses relevant for nutritional status were assessed. Results: Median energy intake was 2,091 kcal/day (range 1,537–3,277 kcal/day). Carbohydrates constituted 59% (range 53–70%) of the total energy, including 15% from added sugar; 26% was from fat. The total protein intake was 1.02 g/kg/day (range 0.32–1.36 g/kg/day), including 0.74 g/kg/day (range 0.13–1.07 g/kg/day) from protein substitutes. Median dietary Phe intake was 746 mg/day (range 370–1,370 mg/day). Median serum Phe was 542 μmol/L (range 146–1,310 mg/day). Fortified protein substitutes supplied the main source of micronutrients. Iron intake was 39.5 mg/day (range 24.6–57 mg/day), exceeding the upper safe intake level. Intake of folate and folic acid, calculated as dietary folate equivalents, was 1,370 μg/day (range 347–1744 μg/day), and resulted in high blood folate concentrations. Median intake of vitamin B(12) was 7.0 μg/day (range 0.9–15.1 μg/day). Conclusions: The diet supplied adequate protein and energy. Fortification of the protein substitutes resulted in excess intake of micronutrients. The protein substitutes may require adjustment to meet nutritional recommendations for adults with PKU