Chronic diarrhea can lead to malabsorption--> resulting in inadequate caloric intake, low levels of essential vitamins, anemia - all of which contribute to fatigue
Causes of chronic diarrhea include: Pancreatic insufficiency (impaired production of key digestive enzymes), chronic inflammation (IBD), other autoimmune diseases (celiac disease, microscopic colitis), Cancer (colorectal, VIP-oma, carcinoid, mastocytosis, lymphoma, gastrinoma, pancreatic), chronic infections (parasites, HIV), Short Gut, post-XRT, medications, hyperthyroidism, niacin deficiency, whipples disease, chronic mesenteric ischemia