The dietary management of phenylketonuria

A wider understanding of the impact of each of the dietary components on blood phenylalanine concentrations in PKU may lead to improvements in management. Knowledge of the effects of such rigorous diet therapy on feeding behaviour is also important. In a series of studies, the effect of a number of dietary factors on plasma phenylalanine control and of diet on feeding behaviour was systematically investigated. The key findings were: 1) there is wide variability in plasma phenylalanine concentrations which were not reflected in a single early morning phenylalanine measurement; 2) plasma phenylalanine concentrations were more influenced by the timing and dosage of protein substitute than by total energy or excess natural protein intake from ‘freely’ allowed foods; 3) repeated 4 hourly administration of protein substitute throughout 24-hours markedly reduced phenylalanine variability and led to lower phenylalanine concentrations; 4) ‘free’ use of fruits and vegetables containing phenylalanine between 51-100 mg/100g did not adversely affect plasma phenylalanine control; and 5) feeding problems were common, with almost 50% of young children with PKU exhibiting at least 3 feeding problems. These findings in PKU are important in the understanding of feeding behaviour; the interpretation of plasma phenylalanine concentrations; they increase and rationalise the range of ‘free’ foods; and will reduce 24-hour plasma phenylalanine variability, and thus, possibly increase dietary phenylalanine tolerance