The nutritional role of fats, oils and the polyunsaturates

Polyunsaturates form a component part of the fats and oils in our food. Such fats and oils are a combination of substances called fatty acids and glycerol (also called glycerine). The fatty acids are long chains of carbon and hydrogen atoms, with a mildly acidic group at one end, which is where they join with glycerol to form molecules called triglycerides. Three fatty acids join with one glycerol, hence the name triglyceride. The various fatty acids which are commonly found in edible oils and fats are classified into three distinct groupings, depending on their actual chemical format. The saturated fatty acids are characteristic of land animal fats, such as butter, tallow (from beef) or lard ( from pigs), and have a high melting temperature (>20o C) which is why such fats tend to be hard at room temperature. The links between the carbon atoms within the chain are single links, which means that the maximum amount of hydrogen is present. More hydrogen cannot be inserted chemically, hence they are termed to be "saturated". Certain fatty acids have some of their carbon-carbon links in a different form, called double bonds. If there is only one such double bond present in a molecule, the fatty acid has a somewhat lower melting point, which usually makes the fatty acid liquid at room temperature. Such fatty acids are called monounsaturated, and are commonly found in certain vegetable oils, e.g. olive oil. Extra hydrogen atoms can be inserted chemically, which is why they are termed "unsaturated". The presence of more than one such double bond makes the fatty acid polyunsaturated. From two to six double bonds can be found in the fatty acids of common edible oils, and the presence of two or more such bonds lowers the melting point even more than with monounsaturates. Vegetable oils such as sunflower oil, and the oils from fish commonly contain high levels of polyunsaturates. Polyunsaturates are further divided into two sub-groups depending on small differences in the way the molecule is made up. The two groups are called omega-6 and omega-3 (sometimes referred to as w-6 or w-3, or even N-6 and N-3). Both of these families of polyunsaturates are essential for good health and normal growth. Since they cannot be manufactured by the human body, they must be supplied in the diet. For this reason, they are often referred to as the " essential fatty acids", or "EFA's"

What we do with oils and fats

The human body uses the oils and fats in the diet for three purposes.

As an energy source

All fatty acids, whether saturated or unsaturated or polyunsaturated contain a high density of carbon and hydrogen atoms. When they are consumed as food, they yield a lot of food energy (37Mj /g, or 9 cals/g) , roughly twice as much as carbohydrates for example. This also means that they are good energy storage materials, providing a lot of energy without taking up too much space. Hence body fat, which is our primary energy reserve, read more