Fats, Fish Oil and Omega-3-Fatty Acids

Medical Author: Dennis Lee, M.D.
Medical Author: Gregory Thomas, M.D.

What is fat?

Fat (also known as lipid), is one of the three classes of nutrients; the other two are proteins and carbohydrates. The major function of fat is to provide energy for the body. Pound per pound, fat contains more energy (calories) than protein and carbohydrates. There are three types of fat:

  1. triglycerides,
  2. cholesterol, and
  3. phospholipids.

Triglycerides are where most of the fat calories are stored. In addition to providing energy, fat also serves other functions, for example, cholesterol and phospholipids are components of cell membranes and sheaths surrounding nerve cells. Cholesterol is also important for the production of bile acids and other hormones (such as sex hormones and adrenal hormones).

What are fatty acids?

Fatty acids consist of chains of carbon atoms linked together by chemical bonds. On one end (terminal) of the carbon chain is a methyl group (a cluster of carbon and hydrogen atoms), the other terminal is a carboxyl group (a cluster of carbon, oxygen and hydrogen atoms). The chemical bonds between carbon atoms can be either single or double bonds. Single bonds have more hydrogen molecules around them than double bonds. These chemical bonds determine whether a fatty acid is saturated or unsaturated (see discussion below). Fatty acids also come in different lengths: short chain fatty acids have less than 6 carbons, while long chain fatty acids have 12 or more carbons.

Fatty acids serve as energy for the muscles, heart, and other organs, as building blocks for cell membranes, and as energy storage for the body. Those fatty acids not used up as energy are converted into triglycerides. A triglyceride is a molecule formed by attaching three fatty acids onto a glycerol compound that serves as a backbone. Triglycerides are then stored in the body as fat (adipose) tissue.

What are saturated fatty acids?

Saturated fatty acids contain single bonds only. Fats containing saturated fatty acids are called saturated fats. Examples of foods high in saturated fats include lard, butter, whole milk, cream, eggs, red meat, chocolate, and solid shortenings. Excess intake of saturated fat can raise one's blood cholesterol and increase the risk of developing coronary artery disease.

What are monounsaturated fatty acids?

Monounsaturated fatty acids contain one double bond. Examples of foods high in monounsaturated fat include avocados, nuts, and olive, peanut and canola oils. Scientists believe that increased consumption of monounsaturated fats (for example eating more nuts) is beneficial in lowering LDL cholesterol (the "bad" cholesterol) and lowering the risk of coronary heart disease, especially if monounsaturated fats are used to substitute for saturated fats and refined sugars.

What are polyunsaturated fatty acids?

Polyunsaturated fatty acids contain more than one double bond. Examples of foods high in polyunsaturated fats include vegetable oils, corn, sunflower, and soy.

What are essential fatty acids?

Essential fatty acids are polyunsaturated fatty acids that the human body needs for metabolic functioning but cannot produce, and therefore has to be acquired from food.

What are omega-3 fatty acids?

Omega-3 fatty acids are a class of essential polyunsaturated fatty acids with the double bond in the third carbon position from the methyl terminal (hence the use of "3" in their description). Foods high in omega-3-fatty acids include salmon, halibut, sardines, albacore, trout, herring, walnut, flaxseed oil, and canola oil. Other foods that contain omega-3-fatty acids include shrimp, clams, light chunk tuna, catfish, cod, and spinach.


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