Physiologically fats are long chains of carbohydrate molecules. The predominant fats in foods and in the body are triglycerides which are made up of three fatty acids attached to a glycerol molecule. Sterols, such as cholesterol and phospholipids, phosphate containing fats are also common. These fats compose the category known as lipids.
Fatty acids are chains of carbon and hydrogen, ending with a so called carboxyl group. The lengths of the fatty acid chain vary from 4 to 24 carbons. The term saturated implies that no more hydrogen atoms can be incorporated into the molecule. The term unsaturated means that there is room for more hydrogen atoms, monounsaturated meaning that there is room for one such atom and polyunsaturated meaning that there is room for more than one atoms. Although so called trans fatty acids may be found in small amounts in nature, they are usually produced synthetically by partial hydrogenation of polyunsaturated fatty acids. This is done in commercial food processing to make liquid oils more solid and to increase the shelf life of the product. A number of studies indicate that trans fatty acids negatively influence cardiovascular risk.
Two 18 carbons fatty acids are essential fatty acids - linolenic and alpha - linolenic acid. The body cannot manufacture these fatty acids, so they must be consumed in the diet. Fortunately, those two essential fatty acid are widely found in food.
From a health perspective, there are certain fats that have been emphasized, because of the proposed effect on the risk of cardiovascular disease. Unsaturated fatty acids such as omega - 3 fatty acids are considered healthy options. Conversely it has been recommended that the consumption of saturated fatty acids be limited and that trans fatty acid consumption be as low as possible due to detrimental effect on the risk of cardiovascular disease.
Usually fats in food are a combination of saturated, monounsaturated and polyunsaturated fatty acids. We commonly tend to identify fat in the food based on the type of fatty acid that is predominant. We know that butter and steak for example predominantly contain saturated fatty acids and olive oil for example contains mainly unsaturated fatty acids.
The polyunsaturated omega - 6 and omega - 3 fatty acids are building blocks for the so called prostaglandins. The prostaglandins play an important role for inflammation in the human body. The omega-3´s are building blocks for anti-inflammatory prostaglandins and the omega-6´s are building block for inflammatory ones. Both these fatty acids therefore play an important role. However, it has been suggested that the overabundance of omega-6 in the western diet compared to omega-3 may be undesirable.
Some studies indicate that consumption of saturated fats may increase blood levels of LDL - cholesterol (the bad cholesterol). There is an association between blood levels of LDL- cholesterol and the risk of cardiovascular disease. Some studies have indicated that replacing saturated fatty acids with polyunsaturated may decrease the risk of heart disease. However, there is indeed very weak scientific evidence linking saturated fat with increased risk for cardiovascular disease.