HDL is good cholesterol and LDL is bad–but WHY?


I know we all get our blood work done and hear about our levels of cholesterol, triglycerides, HDL (high-density lipoprotein cholesterol), and LDL (low-density lipoprotein cholesterol). Maybe you recite the phrase “L stands for lethal and H stands for happy” to remember that LDL is “bad” cholesterol and HDL is “good” cholesterol–But do you know WHY they are considered good and bad? Did you know that your body NEEDS cholesterol to create hormones?

Today I found an excellent video by Jason An on YouTube that describes some key aspects of lipid metabolism. What I liked most about this video is that it gives a pretty clear picture of the relationships between LDL and HDL while still including details I often find are left out. Warning: It is 30 minutes long and has quite a bit of detail, but I think that you will appreciate just how complex and beautiful our bodies really are. Also, the last words in the video that were cutoff are”cardiovascular risk”.

Overview of the video
There are two main pathways: exogenous and endogenous. The exogenous pathway is used when we eat food containing triglycerides (fats) and cholesterol. The endogenous pathway is used for example when cholesterol is produced by the liver.

In the exogenous (exo) pathway, the dietary fats (fats we eat) are taken up in the intestines then the cholesterol and triglycerides are transported through the lymphatic system to the blood stream. Since cholesterol and triglycerides are not soluble in blood, they must be carried by lip
oproteins. Most of the triglycerides are then stored as free fatty acids in the fatty tissue, and the remaining triglycerides and cholesterol are taken to the liver.

From here the endogenous (endo) pathway takes over and cholesterol in the liver is used to make products such as glucose, bile, and steroid hormones (i.e. estrogens). VLDL (very low density lipoproteins) are then formed from the liver and through a series of steps produce LDL. Twenty percent of this LDL is carried to the blood vessels where it may deposit the fat, cholesterol, calcium, and other substances which form plaques that harden and narrow your arteries. This is known as atherosclerosis and is the reason why LDL is considered “lethal” or “bad”.

This is where the “happy” or “good” HDL comes into play–it helps to remove the “bad” LDL cholesterol from your arteries. This is why when you have higher HDL levels, you have a lower chance of having cardiovascular disease. HDL can also remove cholesterol from tissue and take it to the liver, testes, or ovaries to be converted into hormones.

I hope that this has helped you better understand the importance of those numbers in your annual blood work and why what we eat matters. Of course I have left out some fantastic details in this summary, so I encourage you to watch the video and learn even more. Have questions? Ask away!

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