True ileal digestibility of legumes determined by dual-isotope tracer method in Indian adults

BACKGROUND: Good-quality plant protein sources are important for protein adequacy in a balanced diet. Legumes are known to be a source of good quality plant protein, but the true ileal digestibility of indispensable amino acids (IAAs) of commonly consumed legumes is not known in humans. OBJECTIVES: In this study we measured the true ileal IAA digestibility of (2)H-intrinsically labeled chickpea, yellow pea, and mung bean (hulled and dehulled) protein, using the dual-isotope tracer technique referenced to a standard protein ([U-(13)C] spirulina). The study also aimed to validate the use of [U-(13)C] spirulina as a reference protein in this method. METHODS: (2)H-intrinsically labeled legumes, obtained by watering plants with deuterium oxide ((2)H(2)O), were administered in a plateau feeding method to healthy Indian adults to measure their true ileal IAA digestibility with the dual-isotope tracer technique, using [U-(13)C] spirulina protein or a (13)C-algal IAA mixture as the standard. RESULT: The true ileal IAA digestibilities (mean ± SD) of chickpea, yellow pea, and mung bean were 74.6 ± 0.8%, 71.6 ± 1.3%, and 63.2 ± 1.5%, respectively. The true mean ileal IAA digestibility of mung bean when referenced to [U-(13)C] spirulina protein or a (13)C-algal IAA mixture did not differ significantly (63.2 ± 1.5% versus 64.0 ± 2.4%, P > 0.05). The true ileal IAA digestibility of mung bean improved to 70.9 ± 2.1% after dehulling. CONCLUSIONS: The true mean ileal IAA digestibility of legumes in healthy Indian adults was lower than expected. Traditional processing techniques such as dehulling improve protein digestibility by about 8%. This study was registered in the Clinical Trials Registry of India (CTRI): CTRI/2017/11/010468 (http://ctri.nic.in, accessed on 28/03/2019).