For all the bad press that fat gets it actually has some important roles to play in the body. Fat is a source of essential fatty acids and it provides the mechanism for the absorption of fat soluble vitamins (Vitamin A, D, E, K). Fat is also a concentrated energy source, 1 gram of fat providing 37 kJ energy or 9 calories, which is over twice the amount of energy provided by carbohydrate or protein.
In foods, fat carries flavours, enhances the tastiness of foods and assists in satiety or a feeling of fullness after eating.
The health issues associated with fat are related to its excess consumption, especially saturated fat. If excess energy is eaten in the form of fat, it is stored in the body as fat. High levels of fat intake can cause obesity and this increases the risk of diseases such as cardiovascular (heart) disease, type 2 diabetes, hypertension and cancers.
Classification of fats
In general saturated fats are solid at room temperature and are found in animal products, such as butter, full-fat milk and cheese. Coconut and palm oils are an exception to this ‘rule’ as both of these vegetable fats are predominantly saturated. Most meats contain saturated fat although there may also be some monounsaturated fat present.
Saturated fats increase total blood cholesterol and ‘bad’ LDL cholesterol, which promote high levels of fat in the blood and encourage blood clotting. Studies have concluded that a decreased consumption of products containing large amounts of saturated fats decreases the risk of cardiovascular (heart) disease.
Plant foods and seafood are usually a mixture of monounsaturated and polyunsaturated fats.
Monounsaturated fats are most commonly found in olive oil, canola oil, avocado oil, macadamia nuts and almonds. Monounsaturated fats decrease total cholesterol and LDL cholesterol but have no effect on HDL cholesterol, which has a protective effect on cardiovascular (heart) disease.
As with monounsaturated fat, polyunsaturated fats decrease total cholesterol and LDL cholesterol. However, polyunsaturated fats also have an additional positive effect by increasing HDL cholesterol.
There are two essential polyunsaturated fats, Omega 3 and Omega 6, which cannot be synthesised in the body so they must be consumed in the diet. Omega 3 is commonly found in fish and fish oil products, soyabean, walnut and canola. Good sources of Omega 6 are sunflower seeds, soyabean and corn oils. These two polyunsaturated fats are used in the body to make other fatty acids which are important for our well-being. Polyunsaturated fats are important in the body in terms of controlling blood cholesterol concentrations and the body’s immune response.
Trans fatty acids
There has been much media publicity recently about trans fatty acids. Trans fatty acids are commonly found in commercially prepared foods and are formed during hydrogenation of vegetable oils (hardening of the oil with hydrogen) for the production of some margarine. Small quantities of trans fatty acids may also form during deep frying. These fats are unsaturated but they increase total cholesterol and LDL cholesterol, while decreasing the good HDL cholesterol.