Weaning infants with phenylketonuria: a review

Careful weaning is particularly important in phenylketonuria (PKU). Dietary phenylalanine intake is severely restricted, and the diet is supplemented with phenylalanine-free amino acids and special low protein foods. In PKU, there are no evidence-based weaning guidelines and no studies assessing the introduction of solid foods. We critically review the literature and examine current UK weaning practices. Ideally, weaning in PKU should closely reflect the 'model' for healthy infants. However, the requirement for optimal blood phenylalanine control and the demands of diet therapy overshadow the social aspects of weaning. Solid food intake is established with very low protein foods first, and then 50 mg phenylalanine exchanges (equivalent to 1 g of intact protein) gradually replace breast/formula feeds. Introducing solids before the recommended 6 months of age may be advantageous because there is a less persistent neophobic food response, possibly leading to better food acceptance. Infants with PKU also require a special phenylalanine-free protein substitute. Between 6 and 12 months, a second concentrated source of phenylalanine-free protein substitute is required. This is commonly given as an additional liquid, although the prescribed volume may adversely affect appetite. Alternatively, a second-stage protein substitute administered as a paste may better suit feeding development. Further research aiming to examine the weaning process in PKU with a focus on biological, maternal, infant, social and environmental factors is required. This will help provide evidence for the effect of protein substitute on appetite and help in the development of evidence-based guidelines.