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Supplement: Aromatic Amino Acids and Related Substances: Chemistry, Biology, Medicine, and Application: SESSION 4

Aromatic Amino Acid Requirements in Healthy Human Subjects^1–3,

⁴ Research Institute, The Hospital for Sick Children, and Departments of ⁵ Paediatrics and ⁶ Nutritional Sciences, University of Toronto, M5G 1X8 Toronto, Ontario, Canada; and ⁷ Department of Agriculture, Food, and Nutritional Sciences, University of Alberta, Edmonton, Alberta T6G 2P5, Alberta, Canada

^* To whom correspondence should be addressed. E-mail: paul.pencharz{at}sickkids.ca.

Dietary aromatic amino acids are needed to meet the requirements for phenylalanine and tyrosine for protein synthesis. The amounts needed for neurotransmitter synthesis and other biological processes are small and quantitatively negligible. The earlier nitrogen balance-based estimates were judged to be inadequate. Very recently, there have been 3 estimates published based on the indicator amino acid oxidation technique, which average 42 mg·kg^–1·d^–1. This average value was obtained by feeding subjects a tyrosine-free diet and hence is an estimate of the mean maximum phenylalanine requirement. The mean minimum phenylalanine requirement estimate in the presence of an excess of tyrosine is 9.1 mg·kg^–1·d^–1. Hence, tyrosine can spare 78% of the dietary phenylalanine need. Finally the optimal proportions of dietary phenylalanine and tyrosine have been shown to be 60:40, respectively.

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