Chylomicrons: The Major Carrier of Dietary Lipids Into Circulation

January 10, 2026 •

2 min read

Approximately 70-90 grams of dietary lipids are transported by chylomicrons daily, making them the most significant carrier of fats from the intestine. These large, triglyceride-rich lipoproteins are the primary way dietary lipids are packaged and delivered from intestinal cells into circulation.

Quick Summary

Chylomicrons are large lipoprotein particles synthesized in intestinal cells that transport dietary lipids, primarily triglycerides, into the lymphatic system and then into the bloodstream. These carriers deliver dietary fats to tissues for energy or storage before being cleared by the liver.

Key Points

Chylomicrons are Key: Chylomicrons are the primary transporters of dietary fats and fat-soluble vitamins from the small intestine.
Lymphatic Transport: Dietary lipids bypass the liver initially, entering circulation through the lymphatic system via specialized channels called lacteals.
Triglyceride Delivery: Chylomicrons deliver triglycerides to adipose (fat) tissue for storage and muscle tissue for energy, catalyzed by the enzyme lipoprotein lipase.
Intestinal Origin: These lipoproteins are synthesized by intestinal cells (enterocytes) following the digestion and re-esterification of fats within the cell's endoplasmic reticulum.
ApoB-48 Structural Protein: The structural integrity of chylomicrons relies on a unique protein called apolipoprotein B-48 (apoB-48), which is produced in the intestinal cells.
Remnant Clearance: After delivering most of their triglycerides, chylomicrons become smaller remnants that are cleared from the circulation and taken up by the liver.

The Journey of Dietary Lipids

The digestion and absorption of fats are complex processes. Since lipids, such as triglycerides and cholesterol, are insoluble in water, they require specialized transport mechanisms to travel through the watery environment of the body's circulation. This journey begins in the small intestine, where fats are emulsified by bile and digested by pancreatic lipases into fatty acids and monoglycerides. These products are then absorbed by intestinal cells (enterocytes).

Chylomicron Assembly and Secretion

Inside the intestinal cells, a critical transformation occurs. The absorbed fatty acids and monoglycerides are reassembled into triglycerides within the endoplasmic reticulum. These newly formed triglycerides, along with other lipids like cholesterol and fat-soluble vitamins, are then packaged with a protein shell to form a chylomicron. A crucial component for this assembly is apolipoprotein B-48 (apoB-48), which acts as a structural protein. The chylomicron formation process also requires the microsomal triglyceride transfer protein (MTP). If MTP is deficient, chylomicrons cannot be formed, leading to a condition called abetalipoproteinemia.

Once assembled, the nascent chylomicrons are too large to enter the bloodstream directly through the capillaries surrounding the intestine, unlike water-soluble nutrients. Instead, they exit the intestinal cells and enter specialized lymphatic capillaries called lacteals. The lymph fluid, now enriched with chylomicrons, is known as chyle. The lymphatic system then transports the chylomicrons into circulation.

Chylomicron Metabolism in Circulation

Upon entering the bloodstream, nascent chylomicrons acquire additional apolipoproteins, including apolipoprotein C-II (apoC-II) and apolipoprotein E (apoE). ApoC-II activates lipoprotein lipase (LPL), an enzyme that breaks down triglycerides in tissues. Fatty acids released by LPL are absorbed by muscle and fat cells. As triglycerides are removed, chylomicrons become remnants, cleared by the liver.

The Exogenous and Endogenous Pathways of Lipid Transport

Chylomicrons are part of the exogenous pathway, transporting dietary fats to tissues. The endogenous pathway involves VLDL transporting lipids from the liver.

Comparison of Major Lipoprotein Carriers


Feature	Chylomicrons	Very Low-Density Lipoproteins (VLDL)	Low-Density Lipoproteins (LDL)	High-Density Lipoproteins (HDL)
Origin	Intestinal cells	Liver	VLDL metabolism	Liver and intestine
Primary Function	Transport dietary triglycerides to tissues	Transport endogenous triglycerides from liver	Deliver cholesterol to cells	Remove excess cholesterol from tissues
Key Apolipoprotein	ApoB-48	ApoB-100	ApoB-100	ApoA-I
Main Cargo	Triglycerides	Triglycerides	Cholesterol	Cholesterol
Entry to Circulation	Lymphatic system	Directly into bloodstream	From VLDL via bloodstream	Directly into bloodstream

Conclusion

Chylomicrons are vital as the body's main system for delivering dietary fats. These lipoproteins transport triglycerides and other fat-soluble molecules from the intestine into circulation. This process is essential for absorbing and using lipids. For further details on lipid metabolism, refer to {Link: NCBI https://www.ncbi.nlm.nih.gov/books/NBK305896/}.

Frequently Asked Questions

Unlike larger, long-chain fatty acids, short- and medium-chain fatty acids are water-soluble enough to be absorbed directly into the intestinal capillaries and travel via the portal vein to the liver, bypassing the lymphatic system and chylomicron formation.

Chylomicrons are very large lipoprotein particles and are too big to diffuse into the intestinal capillaries, which are smaller. Instead, they enter the more permeable lymphatic capillaries (lacteals), which eventually drain into the bloodstream.

Chylomicrons transport dietary (exogenous) lipids from the intestine, while Very Low-Density Lipoproteins (VLDL) transport internally synthesized (endogenous) lipids from the liver. Chylomicrons are also larger and less dense than VLDL.

Apolipoprotein B-48 (apoB-48) is a crucial structural protein required for the assembly and secretion of chylomicrons in intestinal cells. Each chylomicron particle contains a single molecule of apoB-48, which helps stabilize the lipoprotein and guide its formation.

After delivering their triglycerides, chylomicrons become smaller, cholesterol-rich remnants. The liver recognizes these remnants via apolipoprotein E (apoE) and clears them from the circulation through specialized receptors.

The liver processes chylomicron remnants but is not involved in their initial intestinal absorption.

Genetic defects, such as a mutation in the MTP gene, can lead to a complete inability to form chylomicrons, resulting in conditions like abetalipoproteinemia. This causes a severe deficiency in the absorption and transport of dietary fats and fat-soluble vitamins.