Fats are found not only in foods, but are also added during preparation, cooking and serving. They are essential to your health, but one of the most interesting nutritional discoveries of the past decade has been that not all fats have the same effect on your health.

Saturated fat such as butter, lard and dripping, have been identified as having the potential to increase the risk of cardiovascular disease. They raise the levels of cholesterol in the bloodstream, but other fats, such as monounsaturated and polyunsaturated fats found in plan based oils and fish, are healthy and may protect against disease. So, better start modifying your diet, substitute olive or rapeseed oil for animal fats in your cooking, but remember that whichever oil you choose, it will provide 99 calories per tablespoon. All fats, including oils, should be used in moderation.

Part of group of compounds known as lipids and composed of the elements carbon, oxygen and hydrogen, fats are found mainly in plants, fish and meats. They form major part of all cell membranes in the body and play a vital role in the absorption of the fat soluble vitamins A, D, E and K. Fats givies the body insulation helping to maintain a constant temperature against extremes of hot and cold. Also like an important source of energy.

Lipids and lipoproteins
In addition to fats, lipids include photospholipids, triglycerides, waxes and sterols. The most well know sterol is cholesterol, which circulates in the blood attached to compounds known as lipoproteins. Low density lipoproteins (LDL), which carry cholesterol to tissues and organs (called "bad" cholesterol) since high levels in the blood are associated with an increased risk of cardiovascular disease.

High density lipoproteins (HDL) which carry cholesterol away from tissues and back to the liver (called "good" cholesterol) since high levels decrease the risk of cardiovascular disease.

Fats are also referred to as good or bad according to whether their chemical bonds are saturated with hydrogen. Unsaturated fats are further classified into mono and polyunsaturated, which differ in their nutritional makeup.

Saturated fats
With the exception of palm and coconut oils, most saturated fats are derived from animal and dairy products. Red meat and meat products such as sausages are major sources of saturated fat in the diet along with whole milk, cheese, cream and ice cream.

Intake of saturated fats and trans fatty acids increase the risk of cardiovascular disease by raising the unhealthy LDL levels, so about this they have to be restricted in your diet.

Unsaturated fats

A diet rich in monounsaturated fats like in plant oils, avocados and nuts, helps for lower levels of LDL and triglycerides in the blood, without lowering the healthy HDL levels.

Polyunsaturated fats consist of two major types - omega-3 and omega-6 fatty acids. You should include  both types in your diet. Check the ratio of omega-6 to omega-3

Trans fatty acids

Its occur naturally in small amounts in meat and dairy products, and they also produced during the process of hydrogenation which is used to convert liquid vegetable oils into semi-solid fats in the manufacture of some type of margarine. Trans fats are most found in biscuits, cakes, pastries, meat pies, sausages, crackers and take away foods. Although chemically trans fats are still unsaturated fat, studies show that in the body they behave like saturated fat, causing blood cholesterol levels to rise. Some studies suggest that trans fats are worse than saturated fats.

Both saturated fats and trans fatty acids are bad for you. Saturated fats are almost always found in foods that also contain cholesterol, so saturated fats offer a "one-two" punch to heart health. On the other hand, trans fatty acids not only increase LDL cholesterol, they also decrease HDL cholesterol. So while nobody can say yet definitively which is worse, it does appear that both are bad.

Good fats and bad fats

Some types of fat confer important health benefits. How much fat we need and which types are good and bad. We need to know which foods are high or low of fat, but also we have to identify the different kinds of fats contained on various food and understand why some fats are good for us while another can pose serious health risk.

Which is healthy fat
A diet high in monounsaturated fat reduces the level of bad (LDL) and triglycerides without decreasing levels of good (HDL).  Very low HDL levels, like high LDL levels, increase the risk of cardiovascular disease. Oils high in monounsaturated fat are also especially good for cooking because they develop fewer free radicals than polyunsaturated oils when they are heated.

The two major categories of polyunsaturated fats - omega-3 and omega-6 are known as essential fatty acids since they cannot be synthesized by the body. Omega-3 fatty acids are found in oils from cold-water fish such as tuna, salmon and sardines. They are involved in regulating blood pressure, blood clotting and immune responses as well as for the normal functioning of the brain, spinal cord and the retina of the eye.

Omega-6 fatty acids are found in vegetable oils, such as corn and sunflower oil. This fatty acids are essential for growth cell structure and the maintenance of a healthy immune system.

Read more for ratio of omega-6 to omega-3.

You have to avoid animal fats

Unlike unsaturated fats, which have essential role in your diet, saturated fats are known to increase the risk of cardiovascular disease. These fats come mainly from animal sources, such as meat and dairy products and from certain plant oils. Due to their damaging effects on health, so you should limit the amount of saturated fat in your diet.

Best oil for cooking

All vegetable oils we cook with contain a combination of saturated, monounsaturated, and polyunsaturated fats in varying proportions. In other words, there is no such thing as a saturated-fat-free oil or one containing only polyunsaturated or monounsaturated fat. The dietary difference in cooking oils lies in the proportions each contains of the three basic types of fat. Cooking oil should contain higher amount of monounsaturated and polyunsaturated fats and with minimal or no saturated fats and trans fats. Fully hydrogenated oil does not contain trans fatty acids. Instead, it contains more saturated fat (primarily stearic acid). Stearic acid is immediately converted into oleic acid (a type of mono-unsaturated fatty acids) in our body and that's why stearic acid does not raise LDL cholesterol (the bad cholesterol).

The graph ranks vegetable oils according to their monounsaturated fat contend and will help you make healthiest choices.

Whichever one you choose, remember that oil is 100% fat, and one tablespoon equals 99 calories. If you are trying to control your weight, you should limit all fat intake.

 The oil or fat you use for deep-frying should have a high smoke point — the temperature to which it can be heated without smoking. Butter and margarine have low smoke points, so they aren’t good for frying but work for light sauteing. The best oils for deep-frying and high temperatures are refined safflower and sunflower oils, peanut, safflower and soy oils and canola oil is usually not a problem either.

For deep frying foods: The best oils are those with a high smoke point such as canola oil, corn oil, safflower oil, sunflower oil.

For stir-frying and salad dressing: any oil low in saturated fat like canola oil, corn oil, or flax seed oil, olive oil, peanut oil, safflower oil, sunflower oil and walnut oil.

Oils to avoid: coconut oil, palm oil, butter, hard margarine.

When choosing oil for cooking, look for one with high point of smoking point to minimize the risk of unpleasant odors impaired flavour and reduced vitamin contend. Some oils, such as corn and groundnut are suitable for heating to high temperatures but olive oils is not.

Some have high concentration of monounsaturated fats such as olive oil. Choose corn oil, safflower oil, sunflower oil, soy oil or canola oil if you wish to fry foods as these oils have higher smoke point. It is best not to fry with olive oil as its smoke point is only about 190C/375F.

Unsaturated vegetable oils from canola, peanuts, olive, flax, corn, safflower and sunflower (as long as they have not been subjected to the process of hydrogenation) are heart healthy. These oils contain monounsaturated or polyunsaturated fatty acids that can reduce total cholesterol and increase HDL cholesterol levels. These oils also contain the essential fatty acids - specific fatty acids necessary for life but which the body cannot make itself. (These include omega-3 and omega-6 fatty acids.)

Olive oil is considered by some to be the healthiest oil because it provides a mix of monounsaturated and polyunsaturated fats. It can also be obtained in very pure form, which most health experts recommend. When looking for the healthiest oil, one should look for oils that are minimally processed. Frequently, the more processed the oil, the less healthy it is.
Here is some of the best oil for your cooking:

Canola: According to some studies, it has been linked to negative health effects. But it is all-purpose, and most commonly used in baking and sautéing.

Olive: Ideal for salads, Mediterranean and Italian dishes (like pesto), and of course bread-dunking. Some recommended olive oil brands include: Carapelli, Whole Foods 365 brand, Berio, or the giant Kirkland brand jug from Costco, which should last you months.

Grapeseed: A bit pricy, but keep in mind, grapeseed oil lowers cholesterol. Use it when you'd use olive oil, and since it has a higher smoke point, it's also good for frying and sautéing. (And the super special bottles will involve an elephant spout.)

Peanut: Not the best one for you (lots of monounsaturated fatty acids in there). But when the time comes for stir frying and deep frying, throw a little in.

Sesame: The vitamin E-rich oil adds a nice smoky flavor to foods, especially in meat and chicken. Make sure to keep it in the fridge. Usually the darker the oil, the more sesame-y the taste.

Soybean: It's in so many packaged goods (margarine, salad dressings, and mayo), odds are you're digesting it right now.

Walnut: The FDA is pretty pro-walnuts. They have said that "supportive but not conclusive" evidence shows that "eating 1.5 ounces of walnuts a day ... may reduce the risk of coronary heart disease." So go for it in oil form. Throw walnut oil into salads or finish off a fish dish.

Most experts recommend using peanut oil for high temperature cooking, canola oil or olive oil for medium temperature cooking, and a variety of polyunsaturated oils for baked goods. In a way there is no “healthiest oil” since each oil can offer different benefits and one may be a better choice than another in a cooking process.