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Newborn and Infant Care

PKU and breastfeeding



Should a woman breastfeed a child with phenylketonuria


PKU (phenylketonuria)is a metabolic disorder in which an enzyme necessary for the breakdown of an amino acid (phenylalanine) is either absent on present in inadequate amounts. Amino acids are the building blocks of protein. The deficiency of this enzyme (phenylalanine hydroxylase) results in inadequate breakdown of phenylalanine and excessive accumulation of phenylalanine and metabolites (products of partial breakdown of phenylalanine)in the body. These substances damage the nervous system.

Phenylalanine is found in all proteins, including human milk so that babies with PKU are unable to rely solely on nursing for their nutrition.

Babies with PKU are generally fed a commercial formula which has NO phenylalanine. However, since some phenylalanine is required for normal growth and repair of tissues, some sources of phenylalanine are required. The diet is carefully managed with the formula making up the majority of the diet, with small amounts of protein substances added to supply the required amounts of phenylalanine for growth, but preventing damage from excessive phenylalanine.

With careful management and followup to monitor phenylalanine levels and adjust the amount of phenylalanine in the diet, it is possible for human milk to supplement the diet to provide the allowed amount of phenylalanine. This requires strict monitoring and follow-up.

Answered by Judy Wright Lott, RNC, DSN, NNP

References: Theorell, C. & Degenhardt,M. (1998). Assessment and management of metabolic dysfunction. (pp. 409-475).In Carole Kenner, Judy Wright Lott, and Ann Flandemeyer (Eds.).Comprehensive neonatal nursing:A physiologic perspective. WB Saunders: Philadelphia.

Related Resources:

NSPKU Home Page

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Response by:

Tina   Weitkamp, RNC, MSN Tina Weitkamp, RNC, MSN
Associate Professor of Clinical Nursing
College of Nursing
University of Cincinnati