Small quantities of fats and oils are essential for a balanced diet, but in large amounts they are thought to contribute to ailments such as heart disease. About 45% of the kilojoules or energy value of the average western diet comes from fat. Doctors and alternative practitioners agree that this is far too high, and a figure more like 30% is generally recommended.Reducing fat intake to about this level is particularly important for patients with conditions such as hardening of the arteries, heart disorders or angina. This is because excess fat in the blood stream can build up on the inner walls of the arteries, obstructing the flow of blood and straining the heart and circulation.Low fat diets may also be recommended for obesity, or for people who just wish to lose weight. Weight for weight, fat is the most concentrated form of food energy, containing 37 kilojoules per gram, while proteins, starches and sugars the other main energy giving food components contain only about 16kJ. This means that fat helps to keep us warm and gives us energy for activities. But it is also makes it easy for us to put on weight if we eat a lot of it.Nevertheless, a certain amount of fat is definitely necessary. It contains essential substances known as fatty acids, some of which the body can not make and must get from food. In addition fat containing foods are sources of vitamin A, D,E, and K, and fats can make food tastier.