Fettabsorption

Fettabsorption, or fat absorption, is the process by which dietary fats are digested and absorbed in the small intestine. It primarily involves triglycerides, cholesterol, and fat-soluble vitamins A, D, E, and K. The process begins with emulsification by bile salts released from the liver and gallbladder, which increases the surface area for pancreatic enzymes.

Pancreatic triglyceride lipase hydrolyzes triglycerides into free fatty acids and monoglycerides. These products, along with bile salts and phospholipids, form mixed micelles that transport lipids to the enterocyte brush border. Fatty acids and monoglycerides are then absorbed into enterocytes. Short- and medium-chain fatty acids are more water-soluble and largely enter the portal circulation directly, while long-chain fatty acids are re-esterified to triglycerides within the enterocyte and assembled with cholesterol and apolipoproteins into chylomicrons.

Chylomicrons are released basolaterally into the lymphatic system via lacteals, bypassing the liver on first pass and entering the systemic circulation through the thoracic duct. Bile acids are reabsorbed mainly in the ileum (enterohepatic circulation) and recycled to the liver. Fat-soluble vitamins and dietary cholesterol accompany fats during absorption.

Most fat absorption occurs in the proximal small intestine (duodenum and jejunum). Impairments in fat absorption can result from pancreatic insufficiency, biliary disease, celiac disease, Crohn’s disease, or ileal resection, leading to fat malabsorption and steatorrhea. Diagnostic approaches include fecal fat tests and qualitative staining methods.

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