Luminal

Exocrine pancreatic insufficiency

Lack of pancreatic enzymes (maldigestion)

Luminal

Small-intestinal dysbiosis

• Antibiotic-responsive diarrhea

• Secondary small-intestinal bacterial overgrowth

Bacterial activity: bile salt deconjugation, fatty acid hydroxylation, competition for cobalamin and nutrients

Mucosal

Infectious enteropathies

• Protozoal

• Fungal

• Hookworms

Chronic inflammatory enteropathy

• Inflammatory bowel disease

• Dietary sensitivity

Neoplastic infiltration

Mucosal damage: inflammation, brush border defects, disturbed enterocyte function, reduction of surface area

Mucosal

Villous atrophy

Reduction in surface area, immature enterocytes due to increased cell turnover with reduced brush border enzyme expression

Mucosal

Inherited and acquired brush border enzyme deficiencies

Lactase deficiency, diffuse small-intestinal disease

Postmucosal

Lymphangiectasia

Lymphatic obstruction impairs delivery of chylomicrons

Postmucosal

Vasculitis, portal hypertension

Impaired delivery