Fat should constitute 10-20% of your daily calorie intake. If you are physically active and live in cold climate your fat intake should be higher. In warm climates and with a sedentary lifestyle you need less fat in your diet. Your daily requirements thus range between 15 -60 grams a day of fat in your diet. (1-4 tablespoons).
The body needs a mix of different types of oils for it to function adequately. This should be a mix of saturated oils like coconut oil, mono and di-unsaturated oils like olive oil, peanut oil, mustard oil, sesame oil and polyunsaturated oils like safflower or sunflower oil. Eating only a single type of oil can lead to abnormalities in the levels of different blood fats in the blood.
Unrefined cooking oils are safer for health and should be used in preference to refined cooking oils. However unrefined oils and food cooked in them, tend to go rancid (decompose) faster when stored. Rancid oils have a stale soapy smell. If the oil is rancid return it to the shop from which you bought it or throw it away. Buy oils as close to the date of manufacture as possible and store in a tin or a cool dark place. Consuming rancid oil leads to increased free radical production which causes heart disease and cancer. If any oil or fried food is not being used immediately it should be stored in the refrigerator. Most vegetable oils (both refined and unrefined) decompose in four to eight months at room temperature. Common unrefined oils available are corn, olive, coconut, ground nut (peanut), sesame, sunflower and safflower.
Refined oils are unbalanced oils purified by removing lecithin (which makes it easier to digest absorb & utilize fats), antioxidants like vitamin E & beta carotene (which prevent cancer), phytosterols (which protect the immune system, heart and arteries) and chlorophyll (which contains magnesium necessary for heart, muscle & nerve function). The refining process uses corrosive bases, bleaching acids and clays which may leave residues in the oil. Hydrogenated oils like margarine and dalda (commonly used in India as a substitute for ghee) should be used sparingly as they contribute to raising blood cholesterol when used in large quantities.
Oils made from nuts decompose faster than other oils. However, they can be used a few times for deep frying. Poly unsaturated oils like sunflower, safflower and corn should not be reused for frying. Saturated oils like ghee, coconut oil, animal tallow and palm oil, may be reused a few times for frying. Frying food specially potatoes & reusing the oil leads to formation of acrylamides (a cancer causing substance) in the oil and also in fried foods. High oliec sunflower oil, peanut oil, sesame oil, canola oil and olive oil (in that order) decompose less during cooking. Animal fat like tallow often contains large amounts of hormones and pesticides. Cotton seed oil(BT), rice bran oil, and soya bean oil from Genetically modified seeds contain significant amounts of pesticides which are associated with increased incidence of allergies and cancer and are best avoided. Soya bean oil oil also has a mildly estrogenic effect which can upset your hormone balance!