A 62-year-old man presents with a 6-month history of intermittent, crampy abdominal pain. The pain is localized to the left lower quadrant (LLQ). Episodes last for 1 to 2 days. They recur every few weeks. He notes the pain is not relieved by defecation. It is associated with significant bloating and an alternating pattern of bowel habits between diarrhea and constipation. He denies fever, chills, nausea, vomiting, or rectal bleeding. His last screening colonoscopy 3 years ago was normal except for diverticulosis in the sigmoid colon. His past medical history includes hypertension and obesity with a body mass index of 31 kg/m². His diet is low in fiber. He consumes red meat frequently. He quit smoking 10 years ago. He is a social drinker.