A 32-year-old man with a 10-year history of Crohn disease undergoes surgical resection of a 40 cm segment of terminal ileum due to stricture and perforation. Two weeks postoperatively, he develops watery diarrhea (6–8 stools daily) and steatorrhea. The structure marked **C** in the diagram is responsible for the normal enterohepatic circulation of bile acids. Which of the following best explains the mechanism of diarrhea in this patient?