Review Question - QID 210640

A 32-year-old man with Crohn disease is brought to the emergency department after he fainted at work. He says that he has been feeling increasingly fatigued and weak over the last several weeks though he has not previously had any episodes of syncope. On presentation he is found to be pale and agitated. A panel of lab tests is performed showing the following:

Hemoglobin: 10.2 g/dL
Hematocrit: 30.1%
Leukocyte count: 9,900 cells/mm^3 with normal differential
Platelet count: 290,000/mm^3
Mean corpuscular volume: 118 µm^3
Elevated homocysteine level
Normal methylmalonic acid level

Which of the following mechanisms explains how Crohn disease may have contributed to this patient's symptoms?