Threonine is an indispensable amino acid
for mammals and birds.
However, what has been overlooked for some time is that the Institute of Medicine's (IOM) Food and Nutrition Board published recommended levels for infants, children and adults for nine indispensable amino acids
in its "2002 Dietary Reference Intakes for Macronutrients" report: histidine, isoleucine, leucine, lysine, sulfur-containing amino acids, aromatic amino acids, threonine, tryptophan and valine.
However, the authors state that "whereas lysine is likely to be the most limiting of the indispensable amino acids
in diets based predominantly on cereal proteins, especially wheat, the risk of lysine inadequacy is substantially reduced by the inclusion of relatively modest amounts of animal or vegetable proteins, such as those from legumes and oil seeds or, where appropriate, through lysine fortification of cereal flour.
This new method, called Digestible Indispensable Amino Acids
Score (DIAAS), will measure the digestibility of individual essential amino acids (EAA) in the small intestine as opposed to the previous focus on digestibility of proteins that was determined over the total digestive tract.
The NAS report details the relationship between the various indispensable amino acids
In the current study, we found that, among the indispensable amino acids
, histidine had the lowest apparent digestibility and tryptophan had the highest digestibility within all three groups, whereas, among the dispensable amino acids, the digestibilities of alanine and cystine were the lowest (Table 4).