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Why can inflammatory bowel disease impair nutrient absorption?

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Inflammatory bowel disease (IBD), which includes Crohn disease and ulcerative colitis, impairs nutrient absorption primarily through chronic inflammation of the intestinal wall.12

This impairment occurs because the disease process infiltrates tissues and disrupts the normal function of the small intestine, which is responsible for transporting digested materials into the body. Specifically, inflammation can hinder the work of absorptive cells, disturb intestinal motility, or cause structural damage such as thickening of the intestinal wall and obstruction of the lumen.324

Furthermore, when disease affects the terminal ileum, it specifically interferes with the absorption of vitamin B12 and the reabsorption of bile salts. The resulting interference with bile salts can also disrupt water absorption in the large intestine, leading to diarrhea and further nutrient loss. In severe cases, repeated surgical excisions of diseased intestinal segments can exacerbate this malabsorptive state.52