November 3, 2012
Bringing up baby lipoproteins
A lipoprotein is born as a chylomicron, a particle that your intestinal cells assemble from the proteins and fats you eat. Chylomicrons are very, very low density particles.
Why are some lipoproteins called low density and others high density?
- The term density refers to a lipoprotein’s weight.
- Protein weighs more than fat.
- Lipoproteins containing proportionately less protein than fat are low density lipoproteins, also known as LDLs. LDLs are the “bad” particles that carry cholesterol into your arteries.
- Lipoproteins containing proportionately more protein than fat are high density lipoproteins, also known as HDLs. HDLs are the “good” particles that ferry cholesterol out of your body.
Now, back to chylomicrons. These lipoproteins start out with very little protein and a lot of light and fluffy fat and cholesterol. But as they flow through your bloodstream from your intestines on their way to your liver (your body’s lipoprotein factory), the chylomicrons release their fats, known as triglycerides, into your blood.
The stripped down chylomicron, also known as a chylomicron remnant, still has its cholesterol and protein. Now, the remnant slides into your liver, and fat comes back into the picture.
Shaking Hands with Cholesterol
Cholesterol is the Dr. Jekyll and Mr. Hyde of the nutrition world. This fat-like substance is both essential for your healthy body and potentially hazardous to your heart.
Making the most of cholesterol’s Jekyll-like good characteristics while counteracting its Hyde-like bad impulses can be a delicate but not impossible balancing act. The task begins with understanding how and where cholesterol does its good work and how and where it can cause problems. Begin your mission, in the true scientific spirit, at the beginning.
Where cholesterol comes from
Yes, you get some cholesterol from food, but the curious fact is that most of the cholesterol in your blood and body tissues is produced right in your very own liver. Your liver uses the proteins, fats, and carbohydrates in food to manufacture and churn out about 1 gram (1,000 milligrams) of cholesterol a day.
How cholesterol travels around your body
Whether your cholesterol comes from food or your liver, it travels through your bloodstream in particles called lipoproteins, a name derived from lipos (the Greek word for “fat”) and protos (Greek for “first” or “most important”).
The fatty substances in lipoproteins include cholesterol and triglycerides, the most common fatty substance in the human body (more about triglycerides in the section “Focusing on Other Blood Baddies”). The proteins that combine with fats to produce lipoproteins are called apolipoproteins, often abbreviated as apo.
Lipoproteins develop through five distinct phases as they mature into the particles that carry cholesterol around your body:
- Phase 1: Chylomicrons
- Phase 2: Very low-density lipoproteins (VLDLs)
- Phase 3: Intermediate-density lipoproteins (IDLs)
- Phase 4: Low-density lipoproteins (LDLs)
- Phase 5: High-density lipoproteins (HDLs)
How does a chylomicron become a VLDL, then an IDL, then an LDL, and finally, maybe, an HDL? The following roadmap marks the route.
August 6, 2012
Cholesterol Basics
Cholesterol is a fatty molecule that is manufactured by your liver. You need cholesterol in order to help you manufacture certain types of hormones. However, too much cholesterol circulating through the blood can lead to heart disease.
