Triglycerides: A big fat problem

Content provided by the Faculty of the Harvard Medical School

This forgotten fat is a source of confusion — and heart disease.

Why is it that the most common form of fat in food and in the bloodstream is the one that's most often ignored? Triglycerides take a back seat to low-density lipoprotein (LDL) and high-density lipoprotein (HDL) largely because their precise role in heart disease has been something of a mystery.

That's changing. Researchers are getting a grip on how triglycerides add to atherosclerosis, the artery-clogging process at the root of most heart disease. This knowledge may change how triglycerides are measured and when they need to be treated.

The Trouble with Triglycerides

Good fats, bad fats, and in-between fats have one thing in common: they all contain triglycerides. These particles consist of three fatty acid chains linked by an alcohol called glycerol. When you eat a cheeseburger, your digestive system rips apart the triglycerides in the meat and cheese into their individual fatty acids. These are small enough to enter intestinal cells called enterocytes. Enterocytes stitch together fatty acids into new triglycerides, pack them with protein and cholesterol into huge particles called chylomicrons, and release them into the bloodstream. Chylomicrons ferry triglycerides to tissues, where they are burned for energy or stored. The liver also packages triglycerides into large particles called very-low-density lipoproteins (VLDLs).

As chylomicrons and VLDLs give up their fats to the body's cells, they shrink, becoming dense, cholesterol-rich particles. One of these is LDL, which readily burrows into artery walls. This is a key early step in the process that ends with cholesterol buildup in arteries.

Transformation into LDL isn't the only issue with high blood levels of triglycerides. The more abundant they are, the less HDL the body makes. That's a problem, because HDL scavenges LDL from the blood and from artery walls.

Triglyceride Levels

Classification

Triglyceride level*

Normal

Less than 150

Borderline high

150–199

High

200–499

Very high

500 or higher

*Values in milligrams per deciliter (mg/dL)

Source: National Cholesterol Education Program

Measuring Up

The amount of triglycerides in the bloodstream rises and falls throughout the day. After a fatty meal, triglycerides can be so abundant they give blood a milky tint. Within a few hours, they're mostly cleared out. Doctors traditionally test for triglycerides after an overnight fast so the results aren't thrown off by what you've just eaten. Categories are based on these fasting levels (see "Triglyceride levels").

Two reports in the Journal of the American Medical Association suggest that testing for triglycerides two to four hours after a meal offers a better gauge of their impact on heart disease.

One study followed almost 14,000 Danes for more than 25 years. Women with the highest nonfasting triglyceride levels at the start of the study were five times more likely to have died from a heart attack or other cardiac event than women with the lowest levels. For men, high triglycerides doubled the risk. The second study, conducted by Harvard researchers, followed 26,000 women for more than 10 years. Triglyceride levels measured two to four hours after eating — but not fasting triglyceride levels — were linked with heart attacks and other cardiovascular problems.

It's possible that people who don't clear triglycerides quickly are exposed to their dense, atherosclerosis-causing byproducts for longer than people who get rid of them quickly. It's also possible that triglycerides lingering in the bloodstream is a signal that muscle and other tissues are becoming resistant to insulin.

Reference: Cholesterol section on Better Medicine


Did You Know?

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