Effect of diet on plasma total antioxidant status in phenylketonuric patients

Background: Phenylketonuria (PKU), an inborn error of phenylalanine (Phe) metabolism, is treated with a low Phe lifelong diet, which is a vegetarian and contains many antioxidants. Aim: The aim of this study was to evaluate the effect of diet on plasma total antioxidant status in our PKU patients. Methods, Results: Twenty-two PKU patients on strict diet (group A), 24 PKU patients who did not accurately follow their dietary control (group B) and 40 healthy children (controls) of comparable age took part in this study. Nutrients, as well as blood levels of lipids, vitamin C, β-carotene and α-tocopherol were evaluated in all groups. Vitamin C intake and its blood levels did not differ between the groups. However, the intake of β-carotene, α-tocopherol (2211±116, 14±1.0 mg/24 h) and their blood levels (0.7±0.09, 34±0.9 μmol/l) in group A were statistically significantly higher (P<0.001) as compared with those of group B (1352±118, 10±1.0 mg/24 h and 0.49±0.08, 22±0.6 μmol/l) and controls (1290±120, 9.0±0.9 mg/24 h and 0.40±0.09, 24±1.6 μmol/l). Lipid intakes and their blood levels were lower in patients on the strict diet. Plasma total antioxidant status was higher in the same group of patients (group A). Additionally, positive correlations were found between the antioxidant vitamin blood levels and the plasma total antioxidant status in the groups, especially in the group A. PKU patients of group A showed significantly higher antioxidant status (1.6±0.2 mmol/l) as compared with those of group B (1.0±0.19 mmol/l; P<0.001) and controls (1.01±0.2 mmol/l). Conclusions: The high plasma antioxidant status in patients with PKU, especially in those with a good compliance with their diet, is possibly due to the amounts of antioxidants which are present in their special low Phe vegetarian diet.