Blood 15N:13C Enrichment Ratios Are Proportional to the Ingested Quantity of Protein with the Dual-Tracer Approach for Determining Amino Acid Bioavailability in Humans

Nikkie Van der wielen (1) , Nadezda Khodorova (2) , Walter Gerrits (1) , Claire C. Gaudichon (2) , Juliane Calvez (2) , Daniel Tomé (2) , Marco Mensink (1)

1 WUR - Wageningen University and Research [Wageningen]
2 PNCA (UMR 0914) - Physiologie de la Nutrition et du Comportement Alimentaire

Background: Assessment of amino acid bioavailability is of key importance for the evaluation of protein quality; however, measuring ileal digestibility of dietary proteins in humans is challenging. Therefore, a less-invasive dual stable isotope tracer approach was developed. Objective: We aimed to test the assumption that the 15N:13C enrichment ratio in the blood increases proportionally to the quantity ingested by applying different quantities of 15N test protein. Methods: In a crossover design, 10 healthy adults were given a semi-liquid mixed meal containing 25 g (low protein) or 50 g (high protein) of 15N-labeled milk protein concentrate simultaneous with 0.4 g of highly 13C-enriched spirulina. The meal was distributed over multiple small portions, frequently provided every 20 min during a period of 160 min. For several amino acids, the blood 15N- related to 13C-isotopic enrichment ratio was determined at t = 0, 30, 60, 90, 120, 180, 240, 300, and 360 min and differences between the 2 meals were compared using paired analyses. Results: No differences in 13C AUC for each of the measured amino acids in serum was observed when ingesting a low- or high-protein meal, whereas 15N AUC of amino acids was ∼2 times larger on the high-protein meal (P < 0.001). Doubling the intake of 15N-labeled amino acids increased the 15N:13C ratio by a factor of 2.04 ± 0.445 for lysine and a factor between 1.8 and 2.2 for other analyzed amino acids, with only phenylalanine (2.26), methionine (2.48), and tryptophan (3.02) outside this range. Conclusions: The amino acid 15N:13C enrichment ratio in the peripheral circulation increased proportionally to the quantity of 15N-labeled milk protein ingested, especially for lysine, in healthy adults. However, when using 15N-labeled protein, correction for, e.g., α-carbon 15N atom transamination is advised for determination of bioavailability of individual amino acids. This trial was registered at www.clinicaltrials.gov as NCT02966704.

Mots clés: protein digestibility; stable isotopes; dual-tracer approach; amino acid bioavailability; milk protein; spriulina

Domaines: Alimentation et Nutrition

Nikkie Van der wielen, Nadezda Khodorova, Walter Gerrits, Claire C. Gaudichon, Juliane Calvez, et al.. Blood 15N:13C Enrichment Ratios Are Proportional to the Ingested Quantity of Protein with the Dual-Tracer Approach for Determining Amino Acid Bioavailability in Humans. Journal of Nutrition, 2020, 150 (9), pp.2346-2352. ⟨10.1093/jn/nxaa205⟩. ⟨hal-03010476⟩