The study aims to determine in healthy subjects the bioavailability of protein and amino acids of 4 protein sources: sunflower, rapeseed, lupin, flax. For this purpose, the investigators will compare two methods:

1. the standard method consisting in measuring the ileal digestibility using ileal tubes
2. an alternative method that has been proposed by an Food and Agriculture Organization (FAO) expert group: the dual isotope method

4 groups of healthy volunteers are recruited (males and females from 18 to 65 y old), BMI from 18 to 30.

Each group tests a protein source (20g) incorporated in a biscuit that is divided in small portions to perform a repeated meal protocol. Protein sources (sunflower, rapeseed, flaxseed or lupin) are intrinsically labeled with 15N and deuterium (2H).

The day before the meal test, the volunteers are equipped with an intestinal tube that migrates until the ileum. On the day of the experiment, the position of the intestinal tube is checked by radiography in order to verify its location at the terminal ileum. A catheter is inserted in the forearm vein for blood sampling. A saline solution containing polyethylene glycol 4000 (PEG-4000, 20 g/L), used as a non-absorbable marker of the intestinal flow, is infused into the ileum in order to calculate the flow rate of the intestinal effluents. After a basal blood and urine sampling, as well as a basal collection of ileal effluents performed for 30 min, subject ingests at t=0 the first biscuit dose. The small biscuit portions are ingested every 30 min for 4h, to achieve an isotopic plateau. Tracer doses of carbon 13 (13C) amino acids are ingested concomitantly with the biscuit doses. Non absorbable markers are added to the test meal to correct for incomplete recovery at the ileal level.

The postprandial sampling period lasts for 8 h after the meal ingestion. The intestinal content is continuously collected over ice and pooled every 30 min. Blood is sampled every 30 min for 4 h, and hourly thereafter.Total urine is collected every 2 h.

Measurements:

In the effluents, the investigators measure PEG 4000, nitrogen (N) and 15N, carbon and 13C, amino acids (AA), 15N and 13C in amino acids and the non-absorbable markers of the meal. The investigators calculate the ileal flow rate, the overall real ileal protein digestibility and the real ileal digestibility of individual amino acids.

In the plasma, the investigators measure uremia and 15N in urea, AA and protein to measure the transfer of dietary N in plasma protein pools; 15N, 2H and 13C in individual amino acids too measure the relative bioavailability of 15N/2H amino acids compared to free 13C amino acids.

In the urine, the investigators measure urea and 15N in the urea ammonia to calculate the postprandial deamination losses.

These measurements will allow to determine the protein and amino acid bioavailability from 4 different plant protein sources, using the classical method implying ileal sampling and intrinsic tracer of dietary protein (15N). Additionally, it will allow to test a less invasive procedure using multiple tracers to assess the amino acid bioavailability.

Inclusion Criteria:

• 18<BMI<30
• Healthy
• Insured under the French social security system
• for women: use of birth control
• signed informed consent

Exclusion Criteria:

• Any dietary allergy
• Latex allergy
• Positive serology to HIV, hepatite C virus antibody, hepatite B virus surface antigen and core antibodies
• Gluten intolerance
• Anemia
• Abusive use of drugs or alcohol
• Hypertension, diabetes, digestive disease, hepatic or renal disease, severe cardiac disease
• Pregnancy
• High sport practicing (>7h/wk)
• Blood donation in the 3 months prior to the study
• Participation in a clinical study in the 3 months prior to the study
• No signed informed consent