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What Are Triglycerides and What Do They Do?

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Updated July 13, 2014

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Blood Lipids

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Question: What Are Triglycerides and What Do They Do?

My doctor has told me that my triglyceride levels are elevated. You hear a lot about cholesterol all over the place, but not very much about triglycerides. Can you tell me a little about triglycerides and what they do?

Answer: Triglycerides are a form of fat that the body uses for energy, and they account for the vast majority of fat stored in the human body.

Triglycerides are comprised of one molecule of glycerol attached to three molecules of fatty acids; the entire triglyceride complex consists of long chains of these glycerols, each of which is "carrying" three fatty acid molecules. Triglycerides are named according to the length of the glycerol chains they contain. Some of the names for specific triglycerides you may have heard include oleic acid and palmitic acid.

It is the fatty acids themselves that the body can "burn," as needed, to supply energy to the tissues. So we can think of triglycerides as the body's way of storing and transporting the fatty acids it needs for fuel.

We get our triglycerides from two sources: from manufacturing them ourselves, and from the food we eat.

Triglycerides are synthesized in our liver and by our fat cells. For instance, when we eat excess carbohydrates, the excess carbs are converted to triglycerides. The liver then releases these triglycerides into the blood stream, in the form of VLDL (very low density lipoproteins), where it is taken up by fatty tissues for long-term storage.

Most of the fat we eat—whether from animals or from plants—consists of a mixture of triglycerides. Our intestines cannot absorb the triglycerides themselves, so during the digestive process, the triglycerides in our food are broken down into glycerol and fatty acids, both of which can be absorbed by the cells that line our intestines. Within these intestinal cells, the triglycerides are reassembled, and then released, into our blood stream—along with ingested cholesterol—in "packages" called chylomicrons. The body's tissues then remove the triglycerides from the circulating chylomicrons, either burning it for energy, or storing it as fat. Generally after a meal, the density of chylomicrons in the bloodstream increases for several hours.

This is the reason doctors always ask you to fast for 12 hours before having your blood drawn to measure serum lipid levels. Assessing your risk for cardiovascular disease is based on your "baseline" blood lipid levels—that is, your blood lipid levels at a time when circulating chylomicrons are not temporarily increasing your triglyceride and cholesterol counts.

Since you have been told you have high triglyceride levels, then assuming the blood was drawn while you were in a truly fasting state, your doctor should be doing a full evaluation to find out why. There are several potential (and usually treatable) causes for elevated triglycerides, including diabetes, metabolic syndrome, hypothyroidism, kidney disease, and several prescription medications.

Elevated triglyceride levels are associated with an increased risk of cardiovascular disease, and very high triglyceride levels can produce pancreatitis (a painful and sometimes dangerous inflammation of the pancreas). Depending on the level to which your triglycerides are increased, your doctor may recommend placing you on therapy specifically aimed at bringing down those elevated levels.

Sources:

National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) final report. Circulation 2002; 106:3143.

Triglyceride Coronary Disease Genetics Consortium and Emerging Risk Factors Collaboration, Sarwar N, Sandhu MS, et al. Triglyceride-mediated pathways and coronary disease: collaborative analysis of 101 studies. Lancet 2010; 375:1634.

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