A 52-year-old man has suffered with chronic diarrhea for several years, but has refused to see a doctor. He finally comes because he is having trouble driving at night, because of difficulty seeing. Physical examination reveals a slender, pale, unwell-looking man. He has a microcytic anemia, slight elevation in the INR, low ionized calcium, and albumin levels. Which of the following is the most likely cause for his diarrhea?
malabsorption osmotic diarrhea secretory diarrhea inflammatory bowel disease