Plant proteins are usually less digestible than animal proteins, but they may benefit gut health through effects on the microbiome. The long-term impact of diets rich in plant products on protein digestion and metabolism is still unknown, especially in older adults with higher protein needs. This study aims to compare the digestion and use of pea proteins in young and older adults, both vegetarians and omnivores. Volunteers are divided into four groups: young omnivores, young vegetarians, older omnivores, and older vegetarians. They take part in two clinical investigation days. On the first day, nitrogen retention and protein metabolism is measured after consumption of a pea-based meal. On the second day, amino acid digestibility of pea is evaluated. These results will provide valuable data on how plant proteins are digested and metabolized depending on age and diet. They will also help determine whether aging reduces the availability of plant proteins. This knowledge is important to support nutritional strategies for populations with specific protein needs, such as older adults.
Normal weight or overweight (18 < BMI < 30 kg·m-²)
Male or female
Aged 18-23 years (young groups) or 65-75 years (older groups)
Following an omnivorous diet (regular consumption of meat products, with meat intake > 3 times/week and > 70% of protein intake from animal sources) or vegetarian diet (exclusion of meat and fish/seafood, with > 70% of protein intake from plant sources)
Adults under legal protection or unable to give informed consent (e.g., under guardianship, trusteeship, or legal protection)
Any known food allergy
Positive serology for HBsAg, anti-HBc, HCV, or HIV
Anemia: hemoglobin level < 13 g/dL in men and < 12 g/dL in women
Sequential
Postprandial test
Biological/VaccineA meal containing pea protein labelled with 15N will be eaten by volunteers and dietary nitrogen kinetics will be measured in plasma urea, free amino acids and protein as well as in urinary urea.
Amino acid bioavailability
Biological/VaccineA meal containing pea protein labelled with 2H will be given in a small portions every 30 minutes together with a dose of 13C-labelled amino acid and bioavailability of pea amino acid will be determined with the dual isotopic tracer method.
Pea amino acid bioavailability (%)
During the second inverstigation day, the feeding protocol in portions of the meal (pea protein labelled with 2H and dose of 13C-free amino acids) will make it possible to obtain a plateau of isotopic enrichment in 2H and 13C in plasma amino acid. The ratio of 2H isotopic enrichment to 13C isotopic enrichment for each amino acid in the meal and in plasma, corrected by the digestibility of the reference protein (13C-labeled free amino acid mixture with a theoretical digestibility of 100%), makes it possible to determine the bioavailability (also called digestibility) of amino acids from pea protein in the different groups and expressed as % pea amino acids.
Postprandial desamination of pea protein (%)
During the first day of investigation, the volunteers will eat the meal containing pea protein labelled with 15N and blood and urine samples will be taken. The analyses of 15N enrichment in plasma and urinary urea make it possible to assess the postprandial deamination of the plant protein, reflecting its metabolic bioavailability (expressed as % pea amino acids), in the different groups.
Plasma kinetics of pea protein (%)
During the first day of investigation, the volunteers will eat the meal containing pea protein labelled with 15N. The analyses of isotopic enrichments in the different plasma fractions (protein and free amino acids) make it possible to assess the kinetics of the release of amino acids from the pea protein in the different groups, expressed as % pea amino acids.
Oxydation of 13C amino acid (%)
During the second investigation day, 13C-free amino acids are given with the portionned meals. The analyses of 13CO2 in expired air, combined with CO2 production measured by indirect calorimetry (canopy), make it possible to assess the kinetics of oxidation of 13C-labeled free amino acids in the different groups, expressed as % pea amino acids.
Plasma kinetics of intestinal and metabolic hormones (pmol/L)
During the first day of investigation, postprandial intestinal and metabolic hormones concentration will be measured in plasma samples with ELISA assays: cholescystokinine (CCK, pmol/L), Glucagon Like Peptide 1 (GLP1, pmol/L) and Peptide YY (PYY, pmol/L), Fibroblast Growth Factor 21 (FGF21, pmol/L) and Liver-Expressed Antimicrobial Peptide 2 (LEAP2, pmol/L).
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