An observational study on the true indispensable amino acid digestibility of legume protein in infants

In low- and middle-income countries, legumes are commonly used as a high-quality protein source in complementary foods. However, the digestibility of legume protein in infants might be low because of the immaturity of the digestive system at that age.

The aim of this study was to measure the true indispensable amino acid (IAA) digestibility of mung bean protein in infants aged 10-12 mo.

This was a cross-sectional study in which the IAA digestibility of intrinsically ²H-labeled mung bean protein was measured against U-[¹³C]-spirulina protein as a reference in 6 apparently healthy infants using the dual stable isotope technique. The IAA digestibility of the reference protein, U-[¹³C]-spirulina, was also measured in an additional 3 infants against a ²H-free amino acid mixture.

The mean true IAA digestibility of mung bean protein and that of spirulina protein was 83.6% ± 23.0% and 103.5% ± 33.0%, respectively. These values in infants were higher than those determined earlier in adults (83.6% compared with 63.2% and 103.5% compared with 85.2% for mung bean and spirulina protein, respectively). In mung bean, digestibility ranged from 59.4% ± 11.6% (valine) to 126.5% ± 20.8% (isoleucine) and in spirulina from 46.9% ± 3.3% (valine) to 148.0% ± 17.7% (isoleucine). The digestible indispensable amino acid score (DIAAS) for mung bean protein at this age was 50%.

Infants have a high mean IAA digestibility for mung bean protein, although the generalizability of this finding needs to be confirmed. The estimated DIAAS remains low at 50%. In plant-based complementary foods, a ratio of 1:2 of a legume-cereal mix is required to meet protein requirement in infants at this age. This trial was registered at the Clinical Trials Registry of India as CTRI/2020/09/027639.