Saturated Fats, Monounsaturated Fats and Polyunsaturated F
~ December 1997 No.27 ~
We have to cut down on the saturates in our diet. We have to avoid animal products because they are loaded with saturated fats. Olive oil contains high levels of monounsaturated fat; it’s good for you. Change to canola oil, and soybean oil; they are high in polyunsaturated fats. Fats in our diet come in the form of solid like the white part on a strip of bacon or as a liquid such as a vegetable oil. It is important to point out that it is more correct to say that fats are made up of fatty acids and it is the fatty acids that can be saturated, monounsaturated or polyunsaturated.
Saturated , monounsaturated and polyunsaturated are terms that are almost impossible to avoid these days as nutritionists and dietitians give advice on how to improve our health by changing what we eat. Diet recommendations by government health agencies and specific disease oriented organizations all suggest that we should reduce the total amount of fat in the diet. In addition, changing the types of fat we consume also appears to be prudent.
So what do these words mean, "saturated", "monounsaturated" and "polyunsaturated". To understand you need to know a little chemistry and a little Greek. As for the Greek, un means not, mono means one and poly means many. So we have unsaturates (not saturated), monounsaturates (one unsaturated) and polyunsaturates (many unsaturated). Fatty acids are molecules that contain carbon atoms bonded to other carbon atoms. If all of these carbon - carbon bonds are single bonds then the carbons are said to be saturated. A fatty acid in which all of the carbons are bonded by single bonds is a saturated fatty acid. When two carbons are bonded together by a double bond the carbons are unsaturated. If the fatty acid molecule has one double bond it is a monounsaturated fatty acid; if it contains two or more double bonds in the molecule it is called a polyunsaturated fatty acid.
The change from single to double or triple bonds has a dramatic effect on the structure, chemistry and function in the body of the fatty acid. Structures such as cell wall membranes contain large quantities of polyunsaturated fatty acids. As cells are being formed, the body uses saturated fatty acids if it lacks sufficient amounts of polyunsaturated fatty acids. This could happen if the diet is high in saturated fats and low in polyunsaturated fats. The membrane that is formed will not have the same properties as one made up of polyunsaturated fatty acids. In the long term this can lead to health or disease problems.
Saturated fatty acids and unsaturated fatty acids are metabolized and used differently in the body. Saturated fatty acids are in many of the foods we eat, particularly animal products (meat, milk, butter). In addition the body is able to synthesize saturated fatty acids. Adipose tissue - that layer of fat under the skin - is almost entirely composed of saturated fatty acids. Adipose tissue helps to insulate the body, which is good. But atherosclerotic plaques that form inside blood vessels and can eventually block the flow of blood also are high in saturated fatty acids. Unsaturated fatty acids are found in membrane tissue and are also important building blocks for other compounds in the body such as prostaglandins. Two important unsaturated fatty acids linoleic acid and linolenic acid cannot be synthesized in the body and must be supplied by the diet. These two fatty acids are termed essential fatty acids.
|butyric acid:||oleic acid - one double bond (a mono-unsaturated fatty acid)|
|palmitic acid:||linoleic acid - two double bonds (a poly-unsaturated fatty acid)|
|stearic acid:||linolenic acid - three double bonds (a poly-unsaturated fatty acid)|