Assessment of protein quality is necessary to satisfy the nutritional needs of populations across the world. In addition to indispensable amino acid (IAAs) composition, protein digestibility is a major component of IAA bioavailability, playing a crucial role in human health and affecting the linear growth of children. This study aimed to evaluate IAA digestibility of fava beans, a legume widely consumed in Morocco using the dual-tracer method . 2H-intrinsically labeled Fava beans supplemented with 12 mg/kg BW of 13C spirulina were given to 5 healthy volunteers (3 men and 2 women), aged 25.8 f 3.3 y, with a mean BMI of 20.0 kg/m2. The meal was spread in small portions and was given hourly throughout 7 h. Blood was sampled at baseline and hourly from 5 to 8 h after meal ingestion. IAA digestibility was evaluated by gas chromatogra-phy-combustion-isotope ratio mass spectrometry using the 2H/13C ratio in plasma IAA. Digestible indispensable amino acid ratios (DIAAR) were calculated using the scoring pattern for people older than 3 y. Fava beans had an adequate level of lysine but were limiting in several IAAs, especially methionine. Under our experimental conditions, the average IAA digestibility of fava bean was 61.1% f 5.2%. Valine had the highest digestibility (68.9% f 4.3%) and threonine had the lowest (43.7% f 8.2%). In consequence, the lowest DIAAR was 67% for threonine and only 47% for sulfur amino acids (SAA). The present study is the first to determine the digestibility of fava bean amino acids in humans. The mean IAA digestibility was moderate, and consequently, we conclude that fava bean provides a limited amount of several IAAs, especially SAA, but adequately for lysine. Preparation and cooking methods of fava beans should be improved to increase digestibility. This study was registered at ClinicalTrials.gov as NCT04866927.