Folic acid deficiency due to a low-phenylalanine diet.

A 3-year-8-month-old boy with phonylketonuria who had been placed on a low-phenylalanine diet (“Lofemilk”) developed folic acid deficiency due to a low content of folate in this diet. An oral administration of synthetic pteroylglutamic acid in an amount of 100γ per day was found to be sufficient to meet needs of folic acid for this patient.