Is phenylalanine requirement in infants and children related to protein intake?

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Abstract
1. Two groups of children with phenylketonuria (PKU) received protein at two different levels. The protein scource was a protein hydrolysate, devoid of phenylalanine, and intact protein from milk, vegetables and fruit. One group (RDA group) was given protein at a level based on the recommendations of the (US) Food and Nutrition Board (1974, 1980). The other group (FAO group) was given protein at the level of intake corresponding to the Joint FAO/WHO ad hoc Expert Committee (1973) safe levels of intake of egg or milk protein. The children were monitored very closely for several years. From an earlier study evaluating the protein intake of the two groups it was suspected that the Joint FAO/WHO ad hoc Expert Committee (1973) recommendations were marginal.2. In the present study the phenylalanine intake of the two groups required to maintain the plasma phenylalanine concentration at the required level was established. The results showed that the RDA group required more phenylalanine than the FAO group. This difference was statistically significant from the age of 5–15 months.3. We have interpreted the greater requirement for phenylalanine in the RDA group as a result of a greater nitrogen intake and thus a more rapid chemical maturation of N (increase in protein concentration of the body with age). It is known that up to the age of 6 months the chemical maturation of N is related to the N intake. In the present study we have found that this difference in chemical maturation lasted up to the age of 15 months. The conclusion drawn from the study was that a protein intake slightly higher than the Joint FAO/WHO ad hoc Expert Committee (1973) recommendations might be desirable.