Lipids consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Lipids may be either solid or liquid at normal room temperature, depending on their structure and composition. Although the words “lipids” ,”oils” and “fats” have the almost the same meaning, “oils” is usually used to refer to lipids that are liquids at normal room temperature, while “fats” is usually used for lipids that are solids at that temperature. The word “oil”” is also used for non edible products that does not mix with water and has a greasy feel, such as petroleum (or crude oil) and heating oil, regardless of its chemical structure.
All of them are an important part of the diet of most animals and of human beings. One gram of lipid represents 9 calorie (In nutrition we also say Kilocalorie).
Examples of edible animal fats are lard (pig fat) and butter. Margarine is an artificial fat made either out of lard or of hydrogenated vegetables oils. The supposed benefits of the vegetal based ones over the butter are false, as in the process of hydrogenation lose this benefit: they become saturated. And what is worse, it turns to be a trans fatty acid, that according with the University of Cincinatti (*) is carcinogenic, or cancer-causing.
Examples of oils are olive oil, sunflower oil or peanut oil.
ll lipids contain fatty acids, that can be saturated on unsaturated. This leads to an important distinction between saturated and unsaturated lipids. You have to learn to distinguish between them, as your health depends on it. As a rule of thumb, solid lipids generally are saturated (bad ones for heart). With the oils you have to be more careful. Olive, sunflower, peanut, corn, canola, soy are unsaturated. The olive oil has an advantage. It contains more polyunsaturated fatty acids.
Coconut and palm oil are considered saturated oils.
We are not completely against saturated fat. Mediterranean diet has an small proportion of it, coming essentially from pork and lamb (according with the country). But the olive oil and the high consumption of fish makes the original diet very healthy and balance.
The human body can produce all but two of the fatty acids it needs. They are called “essential fatty acids” This two are the building blocks from which many of the other omega-3 and omega-6 fatty acids are made in a healthy body. They are: Linoleic, an omega-6 fatty acid and alpha Linolenic, an omega-3 fatty acid. These two, are widely distributed in plant oils as the olive one. In addition, fish oils contain the longer-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Although the body to some extent can convert Linoleic and Alpha Linlelic into these longer-chain omega-3 fatty acids, the omega-3 fatty acids found in marine oils help fulfill the requirement of essential fatty acids (and have been shown to have wholesome properties of their own).
(*) In unsaturated fatty acids, there are two ways the pieces of the hydrocarbon tail can be arranged around a C=C double bond. In cis bonds, the two pieces of the carbon chain on either side of the double bond are either both “up” or both “down,” such that both are on the same side of the molecule. In trans bonds, the two pieces of the molecule are on opposite sides of the double bond, that is, one “up” and one “down” across from each other. Naturally-occurring unsaturated vegetable oils have almost all cis bonds, but using oil for frying causes some of the cis bonds to convert to trans bonds. If oil is used only once like when you fry an egg, only a few of the bonds do this so it’s not too bad. However, if oil is constantly reused, like in fast food French fry machines, more and more of the cis bonds are changed to trans until significant numbers of fatty acids with trans bonds build up. The reason this is of concern is that fatty acids with trans bonds are carcinogenic, or cancer-causing. The levels of trans fatty acids in highly-processed, lipid-containing products such as margarine are quite high, and I have heard that the government is considering requiring that the amounts of trans fatty acids in such products be listed on the labels.