A scoping review of the application of the indicator amino acid oxidation (IAAO) method for assessing the metabolic availability of amino acids in legumes

Legumes are good source of plant-based protein, but understanding of their amino acid metabolic availability (MA) remains limited. The indicator amino acid oxidation (IAAO) method is a relatively recent approach for determining the protein quality of foods that is not yet as widely adopted as traditional methods such as fecal and ileal digestibility. This scoping review examined current literature on assessment of metabolic availability (MA) of indispensable amino acids in legumes using IAAO method. Relevant studies published in English, Malay, and Chinese were identified through three databases. Of the ten studies included, three were conducted on animals, while the remaining seven involved human participants, specifically school-aged children and adult men. Legumes examined included peas, faba beans, Amarillo peas, soy protein, chickpeas, lentils, black beans, and cereal-legume-based vegetarian meals. The MA of lysine in legumes was generally high (>80%), whereas methionine showed relatively lower availability (<80%). Although the application of IAAO is still limited in MA determination, IAAO is a valuable and reliable tool for understanding protein quality in plant-based diets and can guide strategies to enhance nutritional outcomes, particularly in populations relying heavily on legumes as a primary protein source.