Our bodies need fats to function healthily. Fats are composed of carbon, oxygen and hydrogen and are present in plants, fish and meat. Their main role is:
1. Insulating the body against extreme temperature changes
2. Formation of cell membranes
3. Source of energy
4. Aiding absorption of fat-soluble vitamins A, D, E and K
There are three main times of fat that we can consume in our diets. They are saturated, polyunsaturated and monounsaturated fats which are similar structurally but have very different effects on the body.  Fat intake should be no more than 35% of our total calories a day and saturated fat less than 10%. A woman consuming a recommended 2000 calories a day should eat less than 73 g of fat and less than 22 g of saturated fat.
Saturated Fats
Saturated fats are triglyceride molecules with fatty acid chains that are saturated by hydrogen molecules. There are deemed unhealthy but are eaten in large quantities by people eating processed food, fast food and ready meals. They clog up arteries and are the main cause of obesity and heart disease. Saturated fat is found in red meat, butter, cheese, lard, pies cakes and biscuits, sausages and bacon and numerous packaged foods. They are solid at room temperature and are used in many commercial processed products to enhance the flavour of the food and to increase shelf life. Most of us eat too much saturated fat - about 20% more than the recommended maximum amount. There are present in a few plant sources but these are deemed to be less harmful. Coconut milk, cocoa butter and palm oil are often in chocolate or cake products. Coconut oil is solid at room temperature and has some healthy benefits and is good for cooking. It is now considered better to use this for frying rather than processed margarines.
Trans Fats
Trans fats increase the risk of high cholesterol and heart disease and strokes. They are made by using heat and pressure to add hydrogen molecules to vegetable oils to make the oil solid. This process gives the product a longer shelf life and enhances flavouring. They have been linked with liver disease, infertility, diabetes and Alzheimer’s so they are to be avoided. They are far worse for you than saturated fats. They are often listed on food labels as emulsifiers, partially hydrogenated oils/fats, shortening or mono and diglyceride fatty acids.
They can be found in all sorts of processed food such as doughnuts, breads, and cakes. Margarines and pastries.  There is a voluntary agreement in the UK to reduce the levels in food and many companies have stopped using them altogether. However they may still be present in many fast food outlets. Some countries such as Canada and Denmark have banned them, which shows how damaging they are.
Unsaturated Fat
Monounsaturated fats are the fats that should be used in cooking. Unsaturated fat can help lower blood cholesterol. It can be found in plant sources such as dark leafy vegetables, nuts and seeds and their oils. Walnuts, Soya beans, fish and avocado are good sources.
Polyunsaturated fats are liquid at room temperature and are found in nuts, vegetable oils and eggs, meat and fish. Cold pressed oils that are in bottles such as walnut, corn and sesame should not be used for cooking as they are damaged by heat. High temperatures damage their bonds, which cause chemicals called free radicals that can damage cells. Cold oils should be stored in a dark place and used for salad dressings and dips. They include Omega 3 and Omega 6 fats, which the body needs for growth and development. Omega 3 fatty acids are found in oily fish such as salmon, tuna and mackerel, avocados, nuts and seeds, sunflower and olive oils Omega 6 fatty acids can be found in seeds, nuts, meats and eggs.  People consuming large amounts of convenience foods are usually deficient in essential fatty acids, as fast food tends to be loaded with saturated fats. These essential fatty acids enhance your immune system and help reduce cholesterol
Cooking with Fat
·    The best cooking oil has a high smoke point, does not break down when heated and has an flavour that enhances the taste of the food
·    All oils are fats.
·    All fat has 9-calories per gram 
There seem to be differing ring opinions as to the best fats for frying. Saturated fat although the unhealthiest is the most stable when heated to high temperature so butter or coconut oil can be used for cooking and if eaten occasionally should not do any damage to your health.
Polyunsaturated fats including vegetable oils such as corn, soy, safflower and canola are to be avoided where possible in cooking as they breakdown when heated producing free radicals linked with cancer and heart diseases.
Monosaturated fats are the healthiest oils in general such as walnut and sunflower and are delicious as salad dressings but are also unstable when heated so to be avoided for cooking purposes apart from Olive Oil.  The International Olive Council state that it is the healthiest of all fats. It is rich in monounsaturated fat, which helps to lower cholesterol levels and reduce the risk of cancer. It's also rich in antioxidants and has a very long storage life. Its best use is cold as a salad dressing or dipping sauce. However, it is also ideal for frying as it undergoes no substantial structural change and keeps its nutritional value better than other oils, not only because of the antioxidants but also due to its high levels of oleic acid. Its high smoking point (210C) is higher than the ideal temperature for frying food (180C). Another advantage of using olive oil for frying is that it forms a crust on the surface of the food that impedes the penetration of oil and improves its flavour. Food fried in olive oil has a lower fat content than food fried in other oils, making olive oil more suitable for weight control. However, Olive oil should never be mixed with other fats or vegetable oils and should not generally be used more than four or five times. It is important to note that oils have a relatively short life and become rancid quickly. It is important to throw away rancid fat, as this can be unhealthy with prolonged use
To conclude we need essential fatty acids for growth and development of all our cells and if we eat good local produce we should get sufficient in our diets. Vegetarians should find them in seeds, nuts, avocados and eggs. Olive oil, coconut oil or organic butter are the safest mediums to fry food as other oils are damaging when heated to high temperatures. Saturated fats in cheese, cream, butter and red meat should be eaten sparingly. Trans fat found in vegetable spreads and many processed goods should be avoided where possible.