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

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