Nutrition Research

Summary

High triglyceride concentration in the blood is associated with an increased risk of developing atherosclerosis and coronary heart disease (CHD). The long-chain omega-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and the B-vitamin niacin (nicotinic acid) have potent triglyceride-lowering effects. Because both nutrients are most effective at high doses, they must be used under a physician’s care.

Condition Overview

Triglycerides are the main type of dietary fat and the most common type of lipid in the body. Like cholesterol, triglycerides can be made in the liver and obtained from the diet.

Dietary Triglycerides

Most of our dietary fat intake (~95%) is in the form of triglycerides. A triglyceride, or triacylglycerol, is comprised of a glycerol molecule with three fatty acids attached. The attached fatty acids may be saturated, trans, monounsaturated, polyunsaturated, or a combination of these.

In fact, all dietary fat and oils are a mixture of fatty acids packaged as triglycerides. Some foods, however, have a higher proportion of a certain type of fatty acid. When a food is said to be high in saturated fat (butter, for example), it means it has a high percentage of saturated fatty acids compared to the other types of fatty acids.

SOURCE: USDA National Nutrient Database for Standard Reference

The type of dietary fatty acids we consume has a major impact on cardiovascular health. High intake of saturated and trans fatty acids has a negative effect on blood cholesterol and is associated with an increased risk of cardiovascular disease. High intake of monounsaturated and polyunsaturated fatty acids has a positive influence on blood cholesterol and is associated with a reduced risk of cardiovascular disease.

Triglyceride Synthesis

Excess calories from our diet are used to make triglycerides that are then stored inside fat tissue. Because they are so easy to consume in excess, simple sugars from refined carbohydrates and sugar-sweetened beverages are a major contributor to triglyceride synthesis in the typical American diet.

High triglyceride concentration in the blood (hypertriglyceridemia) is associated with an increased risk of developing atherosclerosis and an increased risk of coronary heart disease (CHD). See below for specific information about nutrients and dietary factors relevant to high triglycierides.

DEFINITIONS
Lipid - a large class of compounds that are insoluble in water. Lipids include oils, cholesterol, fatty acids, and triglycerides
Triglyceride (also known as triacylglycerol) - a glycerol molecule with three fatty acids attached; triglycerides are the most common form of dietary fat
Fatty acid - a long chain of carbon atoms surrounded by hydrogen atoms; fatty acids differ from each other depending on their chain length (number of carbon atoms) and level of saturation (number of double bonds); fatty acids are classified as saturated, monounsaturated, or polyunsaturated depending on the number of double bonds present
Saturated fatty acid - a type of fatty acid with no double bonds. Saturated fatty acids have a very straight shape and pack tightly together
Monounsaturated fatty acid - a type of fatty acid with one double bond, which introduces a structural kink that prevents tight packing
Polyunsaturated fatty acid - a type of fatty acid with two or more double bonds, which create several structural kinks that create complex shapes and prevent tight packing
Trans fatty acid - a type of fatty acid with one double bond but no kink, therefore creating a very straight, rigid shape and tight packing; the industrial process of hydrogenation leads to the formation of trans fatty acids from unsaturated fatty acids; food with “partially hydrogenated vegetable oil” in the ingredient list contain trans fatty acids

Nutrition Research

DEFINITIONS
Test tube (in vitro) experiment - a research experiment performed in a test tube, culture dish, or other artificial environment outside of a living organism; in vitro is a Latin phrase meaning in glass
Animal experiment - a research experiment performed in a laboratory animal; many different animal species are studied in the laboratory, including terrestrial (land), aquatic (water), and microscopic animals
Observational study - a human research study in which no experimental intervention or treatment is applied, and participants are simply observed over time
Randomized controlled trial - a human research study in which participants are assigned by chance alone to receive either an experimental agent (the treatment group) or a placebo (the control group)
Placebo - a chemically inactive substance

 

Omega-3 Fatty Acids

What they do

General

  • Essential fatty acids are a type of polyunsaturated fatty acid (PUFA). PUFAs have several double bonds in their structure that give them complex shapes and influence their function.
  • Essential fatty acids are structural components of every cell in the body, are converted to compounds that influence inflammation and immunity, and serve as an important source of energy.
  • There are two classes of essential fatty acids: omega-6 PUFA and omega-3 PUFA.

Triglyceride-specific

  • The long chain omega-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), lower triglyceride levels by reducing triglyceride synthesis, increasing triglyceride breakdown in the liver, and by facilitating triglyceride clearance from the blood.
What we know
  • Numerous randomized controlled trials have demonstrated that EPA and DHA, alone and in combination, significantly lower blood triglyceride concentration.
  • The triglyceride-lowering effect of EPA + DHA increases with dose, but clinically meaningful reductions in serum triglyceride concentration have been demonstrated at doses of two grams (g)/day of EPA + DHA.
  • Two to four g/day of EPA + DHA are considered therapeutic doses and should be considered in consultation with a physician.

For references and more information, see the section on Hypertriglyceridemia in the Essential Fatty Acids article. 

There are two essential fatty acids: linoleic acid (an omega-6 polyunsaturated fatty acid) and alpha-linolenic acid (an omega-3 polyunsaturated fatty acid). These fatty acids are considered essential nutrients because they cannot be made in the body and must be consumed in the diet. Vegetable oils, especially safflower oil, sunflower oil, and corn oil, are a good source of linoleic acid.Flax and chia sees, walnuts, canola oil, and soybean oil are good sources of alpha-linoleic acid. Inside body tissues, the essential fatty acids are converted to long-chain fatty acids. Due to low efficiency of conversion, it is recommended to obtain eicosapentaenoic acid (EPA) and docosapentaenoic acid (DHA) from additional sources. Oily fish, fish oil supplements, krill oil supplements, and algae oil supplements are good sources of EPA and DHA.

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Niacin

What it does

General

  • Niacin (vitamin B3) is a B vitamin that assists hundreds of metabolic enzymes and helps convert food into usable energy.

Triglyceride-specific

  • The ways in which nicotinic acid lowers blood lipids (both cholesterol and triglycerides) are still under investigation. Activation of certain receptors inside cells may be responsible for some of its lipid-lowering effects.
What we know
  • Pharmacological doses of nicotinic acid (greater than one gram per day), but not nicotinamide, increase HDL-cholesterol levels while simultaneously decreasing LDL-cholesterol and triglycerides in individuals with abnormal blood lipid levels.
  • Because there are serious adverse side effects associated with high-dose niacin, niacin therapy should only be conducted under the supervision of a qualified health care provider.

For references and more information, see the section on cardiovascular disease in the Niacin article. 

SAFETY HIGHLIGHT

Serious adverse side effects have been observed with use of high-dose niacin supplements.

  • Common side effects include flushing, itching, nausea, and vomiting.
  • Skin rashes, transient episodes of low blood pressure and headache, impaired glucose tolerance, infections, and elevated blood levels of uric acid have been reported.
  • Liver toxicity has resulted with use of nicotinic acid (≥750 milligrams/day) and nicotinamide (≥10 grams/day) supplements.
  • Individuals should only undertake cholesterol-lowering therapy with nicotinic acid under the supervision of a qualified health care provider.

For references and more information, see the safety section in the Niacin article.

Niacin (vitamin B3) Flashcard. Main Functions: (1) helps convert food into useable energy, and (2) assists in DNA replication and repair. Good Sources. Niacin is found in many foods; yeast, meat, cereal, and legumes are especially good sources of niacin. Meat (beef, fish, poultry), chicken (light-meat), 3 ounces, 7.3-11.7 mg. Legumes (beans, peas, lentils), peanuts, 1 ounce (35 peanuts), 3.8 mg; Cereal (fortified), 1 cup, 20-27 mg. Daily Recommendation. 16 mg NE for men, 14 mg NE for women, NE=niacin equivalents, 1 NE=1 mg niacin=60 mg tryptophan. Special Notes. (1) The amino acid tryptophan can be converted to niacin inside the body. (2) Supplemental niacin can cause side effects, such as flushing, itching, nausea, and vomiting; the Tolerable Upper Intake Level (UL) is 35 mg/day. 

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