Protein intake affects phenylalanine requirements and growth of infants with phenylketonuria.

Growth and metabolic status of 25 infants with PKU were evaluated based on protein intake. Food A-fed infants received a medical food containing 3.12 g protein equivalent per 100 kcal and Food B-fed infants received a medical food containing 2.74 g protein equivalent per 100 kcal. Growth percentiles of infants in the Food A group were significantly greater than those for infants in the Food B group at 6 months of age (Food A percentiles: crown-heel length 55, head circumference 60, weight 73. Food B percentiles: crown-heel length 28; head circumference 29, weight 39). At study entrance, only crown-heel length of the two groups differed; Food B infants had a significantly greater mean crown-heel length percentile (p < 0.05). Mean phenylalanine (PHE) intake was 38% greater by Food A-fed infants than by Food B-fed infants. Plasma PHE concentrations and mean energy intakes of the two groups did not differ. Mean protein intake of Food A-fed infants was greater during the first three months of life and significantly greater (p < 0.05) during the second three months of life than by Food B-fed infants. Mean protein intake 24% greater than Recommended Dietary Allowances (RDA) was associated with better PHE tolerance and growth than was found when mean protein intake was 9% greater than RDA.