From the Guidelines
Fat absorption is a complex process that involves the breakdown of triglycerides into fatty acids and monoglycerides, which are then absorbed into enterocytes and re-esterified into triglycerides to form chylomicrons. This process begins in the stomach, where gastric lipase breaks down some triglycerides into fatty acids and diglycerides 1. The majority of fat digestion occurs in the small intestine, where bile salts from the liver emulsify large fat globules into smaller droplets, increasing the surface area for pancreatic lipase to act. Pancreatic lipase, along with colipase, hydrolyzes triglycerides into monoglycerides and free fatty acids, which then form mixed micelles with bile salts and approach the brush border of intestinal enterocytes.
Some key points about fat absorption include:
- Short and medium-chain fatty acids can be absorbed directly into enterocytes and enter the portal circulation
- Long-chain fatty acids and monoglycerides enter enterocytes through passive diffusion or specific transporters like CD36
- Inside enterocytes, these components are re-esterified in the endoplasmic reticulum to form triglycerides, which combine with phospholipids, cholesterol, and apolipoproteins to form chylomicrons
- Chylomicrons are then released into the lymphatic system via lacteals, eventually entering the bloodstream through the thoracic duct
Disorders affecting any step in this process, such as pancreatic insufficiency, bile salt deficiency, or genetic mutations in key transporters, can lead to fat malabsorption and steatorrhea, as seen in conditions like chronic pancreatitis 1. In such cases, pancreatic enzyme replacement therapy (PERT) may be necessary to alleviate symptoms and prevent malnutrition. The formation of chylomicrons and their subsequent transport into the lymphatic system is a critical step in fat absorption, and any disruption in this process can lead to significant morbidity and mortality.
From the Research
Pathophysiology of Fat Absorption
The pathophysiology of fat absorption is a complex process that involves multiple stages and components.
- The initial stage of fat digestion occurs in the stomach, where gastric lipase begins the hydrolysis of triglycerides 2.
- Most fat digestion takes place in the small intestine via pancreatic enzymes and bile salts, with emulsification of fat by bile acids facilitating enzymatic action 2, 3.
- The products of lipolysis, monoglycerides and fatty acids, are removed from the emulsion surface by bile salts in the form of mixed micelles, which transport lipid digestive products across the unstirred water layer to the epithelial cell 3, 4.
- Within the intestinal epithelial cell, a series of synthetic events occur, resulting in the formation of chylomicrons and very low-density lipoprotein (VLDL) 4.
- Chylomicrons consist of an oily core of triglyceride surrounded by a membrane of phospholipids, free cholesterol, and apoproteins, which maintain the solubility of the particle in plasma 4.
Fat Malabsorption
Fat malabsorption can result from various underlying conditions, such as:
- Exocrine pancreatic insufficiency 2
- Bile acid disorders 2
- Intestinal diseases 2
- The clinical manifestations of fat malabsorption include steatorrhea, malnutrition, and deficiencies of fat-soluble vitamins 2.
Diagnostic Approaches
Diagnostic approaches for fat malabsorption involve: