Low-density lipoprotein (LDL)

Last Updated: August 16 2022

LDL carries cholesterol from the liver to other parts of the body. Because higher levels of LDL cholesterol (LDL-C) tend to increase the risk of cardiovascular disease (CVD), LDL-C is often called the “bad cholesterol” (as opposed to HDL-C) — but the reality is more complex.


Low-density lipoproteins (LDL) are proteins that carry hydrophobic molecules through extracellular fluid. More precisely, they carry cholesterol from the liver to other parts of the body, via the bloodstream.

The greater the number of LDL particles (LDL-P) in the blood, the more likely some will pass into artery walls, become oxidized, and kickstart plaque formation,[1] leading to atherosclerosis. Therefore, to predict cardiovascular disease (CVD), LDL-P matters more than LDL cholesterol (LDL-C),[2][3] which is simply a measure of the amount of the cholesterol carried by LDL particles.

If two people have the same LDL-C but one has cholesterol-rich LDL (large, “fluffy” particles) and the other cholesterol-poor LDL (smaller, denser particles), the second will have a greater LDL-P (more LDL particles total) and be at greater risk of heart disease.

While a WHO meta-analysis of saturated fat didn’t cover LDL-P,[4] it did report the levels of apolipoprotein B (apoB), the protein component of LDL. Since each LDL particle has one molecule of apoB, apoB concentrations provide a good estimate of LDL-P concentrations and are a strong predictor of heart disease risk.[5][6]

To predict heart disease, LDL-P (the number of LDL particles) matters more than LDL-C (the amount of cholesterol those particles carry). There is one molecule of apolipoprotein B (apoB) in each LDL particle, so apoB is a good estimate of LDL-P.

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