Effect of Vegetarien Diet on Protein Digestibility in Young and Elderly Volunteers (VEGAA)

Effect of a Vegetarian Diet on the Bioavailability of Amino Acids From Plant Protein in Healthy Young and Elderly Volunteers (VEGAA)

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.

Study Overview

• Status: Recruiting
• Conditions: Elderly; Vegetarian Diet; Young Healthy Adults
• Intervention / Treatment: Biological: Postprandial test; Biological: Amino acid bioavailability

Detailed Description

Plant proteins generally have lower digestibility than animal proteins but also provide positive effects on the digestive system, particularly on the gut microbiota. However, the long-term effects of consuming a diet rich in plant-based products on protein digestion are still unknown. In the context of the nutritional transition toward more plant-based diets, it is important to comprehensively study the effect of such diets on the bioavailability of plant proteins. This is especially relevant for populations with specific protein needs, such as older adults.

The aim of the study is to compare the digestive and metabolic bioavailability of pea proteins in young and older adults, vegetarians and omnivores.

Peas are labeled with stable isotopes (15N and 2H), which are completely safe for health. Four groups of 8 healthy volunteers (+ 4 possible dropouts) are recruited according to age and dietary habits: young omnivores (18-23 years), older omnivores (65-75 years), young vegetarians, and older vegetarians. The volunteers' diets are characterized using an online food frequency questionnaire.

Each volunteer participates in two clinical investigation days, separated by 4 weeks to 2 months. On the first investigation day, a postprandial test is conducted after ingestion of a pea-based meal (100 g dry weight) labeled with 15N, consumed in normal conditions (as a bolus). Blood samples are taken regularly over 8 hours (156 mL total), and urine is collected every 2 hours. Postprandial kinetics of plasma amino acids concentrations, incorporation of dietary nitrogen in plasma protein and free amino acids as well as plasma gut hormones and protein metabolism markers are determined. Desamination of dietary protein is evaluated through determination of dietary nitrogen in plasma and urinary urea.

On the second investigation day, participants undergo the dual isotope tracer method to assess the digestibility of amino acids from pea proteins. They consume a pea-based meal (100 g dry weight) labeled with 2H, distributed in portions every 30 minutes for 7.5 hours. Free amino acids labeled with 13C are added to each portion. Blood samples are collected regularly over 8 hours (130 mL total). Respiratory exchanges are measured by indirect calorimetry in 15-minute periods every hour, and breath samples are collected regularly. 2H and 13C enrichment in individual amino acids are determined in plasma from 5 to 8h during a plateau. Oxydation of 13C amino acids is evaluated through measurement of 13CO2 in expired air.

The results will provide data on the digestive and metabolic bioavailability of plant proteins and amino acids in young and older individuals, whether vegetarian or omnivore. This study will therefore contribute to advancing knowledge about the digestibility of plant proteins and how it changes with aging, a question for which little data is currently available.

• Study Type: Interventional
• Enrollment (Estimated): 48
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Juliane Calvez, PhD; Phone Number: +33189100875; Email: juliane.calvez@agroparistech.fr

Study Locations

• France
  • Bobigny, France
    • Recruiting
    • Centre de Recherche sur Volontaire, Hopital Avicenne (AP-HP)
    • Contact: Juliane Calvez, PhD; Phone Number: +33189100875; Email: juliane.calvez@agroparistech.fr
    • Contact: Suzette Maurinier; Phone Number: +33148957433; Email: suzette.maurinier@aphp.fr
    • Principal Investigator: Robert Benamouzig, Pr

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• 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)
• In good general health (WHO = 0)
• Affiliated with a social security system
• Free and informed consent, provided in writing after receiving the information required by the Public Health Code

Exclusion Criteria:

• 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
• Pregnant women or those who may be pregnant (based on a positive urine pregnancy test at inclusion)
• Excessive alcohol consumption (> 2 drinks/day). Harmful alcohol use will be assessed by the investigator at inclusion.
• Hypertension, diabetes, gastrointestinal, liver or kidney diseases, or severe heart disease. These conditions will be assessed by the investigator based on standard clinical evaluation and participants' self-reports at inclusion.
• Hypertension: significant arterial hypertension according to the investigator, or systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg at inclusion.
• Diabetes: type 1 or type 2 diabetes, or fasting blood glucose > 1.25 g/L.
• Gastrointestinal disease: clinically significant gastrointestinal disorders (bleeding, vomiting, constipation/diarrhea grade > 1) as judged by the investigator, any inflammatory bowel disease, or acute gastroenteritis in the month prior to the intervention.
• Liver disease: any significant hepatic disorder according to the investigator, or ASAT/ALAT > 2.5 times the upper normal limit.
• High-level athletes (> 8 hours of training per week)
• Blood donation within 8 weeks prior to study start
• Absence of free, informed, written consent after receiving the information required by the Public Health Code
• Not affiliated with a social security system

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Non-Randomized
• Interventional Model: Sequential Assignment
• Masking: None (Open Label)

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Young adult, vegetarian; Young adult (18-23 years) with a vegetarian diet: exclusion of meat and fish/seafood, with > 70% of protein intake from plant source	Biological: Postprandial test; A 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.; Biological: Amino acid bioavailability; A 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.
Experimental: Young, omnivore; Young adult with omnivorous: regular consumption of meat products, with meat intake > 3 times/week and > 70% of protein intake from animal sources	Biological: Postprandial test; A 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.; Biological: Amino acid bioavailability; A 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.
Experimental: Old adult, vegetarian; Old adult (65-75 years) with vegetarian diet: exclusion of meat and fish/seafood, with > 70% of protein intake from plant sources	Biological: Postprandial test; A 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.; Biological: Amino acid bioavailability; A 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.
Experimental: Old adult, omnivorous; Old adult (65-75 years) with omnivorous diet: regular consumption of meat products, with meat intake > 3 times/week and > 70% of protein intake from animal sources	Biological: Postprandial test; A 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.; Biological: Amino acid bioavailability; A 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.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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.	From the begining of the second investigation day (8:00) to 8 hours after the first meal intake (around 18:00).

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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.	From the begining of the first investigation day (8:00) to 8 hours after the first meal intake (around 18:00).
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.	From the begining of the first investigation day (8:00) to 8 hours after the first meal intake (around 18:00).

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
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.	From the begining of the second investigation day (8:00) to 8 hours after the first meal intake (around 18:00).
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).	From the begining of the first investigation day (8:00) to 8 hours after the first meal intake (around 18:00).

Collaborators and Investigators

• Sponsor: Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement

Study record dates

Study Major Dates

• Study Start (Actual): October 22, 2025
• Primary Completion (Estimated): December 31, 2026
• Study Completion (Estimated): December 31, 2026

Study Registration Dates

• First Submitted: September 23, 2025
• First Submitted That Met QC Criteria: April 7, 2026
• First Posted (Actual): April 9, 2026

Study Record Updates

• Last Update Posted (Actual): April 9, 2026
• Last Update Submitted That Met QC Criteria: April 7, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Keywords: Elderly; Plant protein; Vegetarian diet; Amino acid bioavailability; Protein utilization; Isotopic method
• Other Study ID Numbers: VEGAA

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No