The True Amino Acid Digestibility of 15N-Labelled Sunflower Biscuits Determined with Ileal Balance and Dual Isotope Methods in Healthy Humans

Abstract

Background Sunflower is a promising protein source but data on amino acid (AA) digestibility are lacking in humans. Classically, the determination of AA digestibility requires ileal digesta sampling. The dual isotope method is minimally invasive but has not been compared to the conventional approach. Objective This study aimed to determine the true ileal digestibility of sunflower AAs in healthy volunteers who ate biscuits containing 15N protein isolate, in comparison with the dual isotope method. Methods Twelve healthy volunteers (men and women, 40.4±10.5 years old, BMI 23.7±2.9 kg/m2) were equipped with a naso-ileal tube. They consumed for 4h nine repeated meals comprising 15N-sunflower protein biscuits together with 13C-AAs, carried either in chocolate (SUN+C, n = 7) or apple puree (SUN+P, n = 5). Ileal digesta and blood were sampled throughout 8h after ingestion of the first meal. The 15N and 13C AA enrichments were measured in digesta to determine ileal digestibility directly, and in plasma to determine lysine and threonine digestibility using the dual isotope method. Differences between methods and between vector groups were analyzed using paired and unpaired t-tests, respectively. Results Ileal digestibility of sunflower indispensable AAs (IAA) was 89±5.3%, threonine and lysine having the lowest digestibility. In the SUN+C meal, IAA digestibility was 3% below that of SUN+P (P < 0.05). Mean free 13C-AA ileal digestibility was 98.1±0.9%. No matter which matrix was used to carry 13C-AAs, plasma 15N and 13C-AA kinetics displayed a 1h offset. Digestibility obtained with the dual isotope method (70.4±6.0% for threonine and 75.9±22.3% for lysine) was below the target values. Conclusions The ileal digestibility of IAAs from a sunflower isolate incorporated in a biscuit was close to 90% in healthy adults. Under our experimental conditions, the dual isotope method provided lower values than the usual method. Further protocol developments are needed to validate the equivalence between both methods. Clinical Trial Registry The clinical trial was registered at www.clinicaltrials.gov database (NCT04024605).

True Ileal Amino Acid Digestibility and Protein Quality of 15N-Labeled Faba Bean in Healthy Humans

“…The discrepancies between these results may be due to the different cultivars, as discussed later, and to the different methods used. It has been speculated that the dual isotope method underestimates the IAA digestibility compared with the ileal balance method [ 35 , 36 ], but another internal comparison study does not support this systematic underestimation [ 37 ] as sometimes the dual isotope method seems to overestimate and sometimes underestimate digestibility compared with the direct method. Regarding legumes, no internal comparison exists; thus, external comparisons include the effect of the model or method and the effect of the cultivar.…”