Congenital metabolic diseases are not rare in Turkey. For instance, phenylketonuria frequency is 1/4500. Classic phenylketonuria occurs as a result of deficiency of phenylalanine hydroxylase which is a liver enzyme. If it is not treated, the most serious clinical finding of it is mental retardation. Signs of disease can be prevented with early and effective treatment. Basic treatment is nutrition therapy in which low protein and low phenylalanine medical foods are used. Methods such as protein precipitation from whey, amino acid disposal and adding free amino acids, vitamins and minerals to isolated soy protein or whey protein can be used in order to produce low protein product. We preferred the last method in the present study. We indicated via food analysis that product contains adequate nutrients. We demonstrated in experimental animals that consumption is at safe limits in terms of phenylalanine. It is necessary to continue the study in order develop and make the product suitable for use among human beings.