Triglycerides: Definition, Structure, Sources and Unknown Facts

This post gives a comprehensive description of what triglycerides are, their medical definition in simple words, their chemical structure and how it relates to their functions, how does the body procure them (meaning their sources), how they are metabolized or broken down in the body and their classification.

What are triglycerides? Definition 

Triglycerides are chemical compounds, which are present in the body and certain foods. In the body, they are present in the blood plasma in the form of VLDL (Very low-density lipoproteins) to be transported for storage in the fat cells or to be utilized by the cells throughout the body.

Along with cholesterol, they form the lipid profile or the lipid panel of the blood. Most of the fat stored in the human body is in the form of triglycerides.

In foods, they are the main constituents of natural fats and oils.

Though they are seen about as bad for health by the general population, they do perform certain important functions in the body. However, it is their high levels in the blood that can cause serious complications. Check out their healthy and undesirable levels.

  • Healthy levels in the blood should be less than 150 mg/deciliter (d/L).
  • Borderline levels are 150 to 199 mg/dL.
  • High values fall between 200 to 499 mg/dL.
  • Very high levels are 500 mg/dL and greater.

Due to their functions, a normal intake of triglycerides via diet is required. Avoid excessive consumption of foods that are rich in saturated fats. This will keep their blood numbers within the normal limits and you, out of the danger zone.

How are triglycerides formed in the body? Their sources 

Your body gets triglycerides from the foods that we eat and they are also produced in the liver and the fat cells.

From foods

Vegetable oils such as sunflower and peanut oils and meat and dairy products are the rich sources of triglycerides. Such foods are also rich in saturated fats (the unhealthy fats) and LDL cholesterol (the bad cholesterol).

Besides elevating levels of triglycerides, they lower the levels of HDL, the good cholesterol, which protects your heart from the ill effects of LDL and triglycerides.

Examples of such foods to restrict are fatty red meat, butter, lard, shellfish, poultry skin, and high-fat dairy products.

Sources within the body

Triglycerides are manufactured in the body by the liver from the fats and carbohydrates obtained through the foods that we eat.  They are also synthesized by the body’s fat cells. Therefore, a diet high in fats and/or carbohydrates can increase your triglyceride levels.

They are stored as adipose tissue in fat cells for later use. Lipids form about 80% of the white adipose tissue and of that, about 90% are triglycerides.

The six types of fatty acids that make up the bulk of the triglycerides in the body are:

  • Stearic acid
  • Oleic acid
  • Linoleic acid
  • Palmitic acid
  • Palmitoleic acid
  • Myristic acid

Besides triglycerides, also stored are free fatty acids, cholesterol, monoglycerides and diglycerides.

When your body requires them for energy, triglycerides are released as fatty acids, which provide energy for various body activities and production of heat.

The fat cells use them to produce adenosine triphosphate (ATP), which is the main energy source of the cell.

Structure of triglycerides: Glycerol and fatty acids

To understand triglycerides and their composition, you should first know what are lipids and fats.

Lipids are naturally occurring molecules and include fats, sterols, fat-soluble vitamins, monoglycerides, diglycerides, phospholipids and others.

Fats are a form of lipids and are chemical compounds that dissolve in organic solvents but are not soluble in water. They consist of glycerol and fatty acids. Lipids or fats are present in food as phospholipids (lecithin), sterols (cholesterol) and triglycerides.

Triglycerides are the most common type of fats in the body.

Their structure and properties are related to their functions; in other words, they are structured in such a manner so as to help them perform their valuable functions in living organisms.

Triglycerides are also called triacylglycerol (TAG), and their chemical structure consists of a long chain of one molecule of alcohol glycerol attached to three building blocks consisting of three molecules of fatty acids through ester bonds.

Glycerol forms the backbone of the triglyceride molecule and the three fatty acids form the “tri” of triglycerides.

The structure of each of the three fatty acids within a single triglyceride molecule often differs, but they are all long chains of carbon atoms with bonded hydrogens. It is the number of hydrogen atoms in each fatty acid that determines the physical properties of the triglyceride.

The result is a wide diversity of compounds: Monoglycerides, diglycerides, and triglycerides. It is the fatty acid component of that is responsible for the production of energy required by the body.

How does the triglycerides structure relate to their functions?

Triglycerides are an important source of metabolic water due to the fact that triglyceride molecules yield water on getting oxidized. This is particularly helpful in desert animals such as the camel. Even migratory birds rely on metabolic water while flying nonstop over long distances.

Metabolic water is water created inside a living organism through metabolism, by oxidizing the energy-rich substances in their food.

Again, triglycerides are poor conductors of heat, this helps them to act as heat insulators and preserve heat in the body. This is especially helpful to animals living in extremely cold climates such as the polar bears.

The triglyceride molecule possesses low mass and yet is a powerful provider of energy. This is particularly useful in animals requiring movement and mass to be kept to a minimum.

Finally, triglycerides are less dense than water. In aquatic mammals, this helps to give them buoyancy.

Types: Saturated and unsaturated

Triglyceride fatty acid tails can be saturated or unsaturated.

Saturated fatty acid tails are all single bond carbons, which mean that for every carbon there are two hydrogens and two carbons attached. These are the fatty acids that are solid at room temperature and increase your cholesterol and risk of heart problems.

Unsaturated fatty acids tails have at least one double bond. Those with one double bond are called monounsaturated and those with more are called polyunsaturated fatty acids. Unsaturated fatty acids are liquid at room temperature and promote the health of your heart.

Triglycerides can be solid or liquid at room temperature. Solid triglycerides are called fats or “butters”, while the liquid triglycerides are known as oils.

How are triglycerides metabolized or broken down?

Once the triglycerides are in the bloodstream, they are stored in the adipose tissue to be used for energy production when the body requires it.

Secondly, they are also utilized by the cells. They move on the surface of the tissue cells throughout the body. But, triglycerides cannot pass through the cell membrane (outer covering of the cell) freely.

To facilitate this entry, special enzymes called lipase lipoproteins are released from the wall of the blood vessels, which break down triglycerides into glycerol and fatty acids. Fatty acids are then taken up by the cells via the fatty acid transporter (FAT, in short).