GLOSSARY

Phenylalanine is an essential aromatic amino acid and tyrosine precursor. Its conversion role does not remove the need for sufficient dietary phenylalanine.

Common nutritional groupings call phenylalanine, tyrosine and tryptophan aromatic amino acids. Histidine's imidazole ring is chemically aromatic too, although teaching schemes may place it separately. Aromatic describes ring electronic structure, not necessarily a food's smell or an ergogenic property, so the classification convention needs to be understood.

The body synthesises some amino acids from other precursors: tyrosine can come from phenylalanine and cysteine synthesis uses methionine. These relationships still require precursors and suitable conditions. Making a nonessential amino acid does not mean that any amino acid can be converted into every essential one when dietary supply is lacking.