FIGURE 1.

Schematic representation of the principle of the oro-ileal balance method to measure ileal AA digestibility with (A) intubated healthy volunteers or with (B) ileostomized patients using labeled protein. With the intubation method, the volunteers are equipped with a triple lumen naso-ileal tube. One lumen is dedicated to inflate a balloon at the end of the tube to facilitate the migration of the tube through the intestinal tract. When the tube is at the terminal ileum, a perfusion of PEG (unabsorbable marker) is started through the second lumen, in order to evaluate intestinal flow by the slow marker method. The test meal containing intrinsically ¹⁵N-labeled test protein undergoes digestion and absorption and ileal effluents containing nonabsorbed dietary AAs are continuously collected from the third lumen during the 8-h postprandial period. In ileostomates, where the colon and rectum have been partially or totally removed and the terminal ileum exteriorized, the ileal effluents are directly collected into the pouch. The digestibility of each AA is determined by the ratio of the absorbed AA to the intake. AA, amino acid; PEG, polyethylene glycol.