Lipids are calorific substances that are insoluble in water but highly soluble in organic solvents such as acetone. Generally, lipids that are in the solid state in room temperature are categorized as fat and and those that are in the liquid state are categorized as oil. Lipids include fatty acids, triglycerides, phospholipids, cholesterol and fat-soluble vitamins, etc. Among these, triglycerides take up over 90% of all natural lipids.
Fatty acid is a type of lipid that has the chemical structure of a single chain of carbon that starts from the carboxyl group (COOH-) and ends with methyl group(CH3-). Its chemical structure is similar to the shape of a centipede. Fatty acids whose carbon atoms form a tightly held-tougher single chain without the double bond are called saturated fatty acids. When carbon atoms are held together with double bond, they are held together loosely and this type of fatty acid is called unsaturated fatty acid. Therefore, saturated fatty acid is in the solid form (fat) in room temperature, whereas unsaturated fatty acid is often in the liquid form (oil)
The important aspect of saturated fatty acid is the number of carbon atoms. Depending on the number of carbon atoms, the saturated fatty acid is divided into short chain fatty acids (2-4 carbon atoms), medium chain fatty acids (4-12 carbon atoms), and long chain fatty acids (12 carbon atoms). The length of the carbon chain is important because the fatty acids behave differently depending on it. Short chain fatty acids usually form trans fat. Medium chain fatty acids are not stored in the body but easily converted to an energy source and as such, they do not cause weight gain. Coconut oil is a well-known example of this type. Long chain fatty acids partially convert to energy source and get stored as fat. Animal fat and soybean oil fall in this category.
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Unsaturated fatty acids are not produced in the human body and needs to be supplemented, making them essential fatty acids. The methyl group lies at the tail of the chemical structure and this is called the omega end. These fatty acids are called omega 3, 6 and 9 depending on how many carbon atoms are counted from the end up to the double bond. Omega 3 means the double bond lies between the third and fourth carbon atoms.
Omega 3 is mainly categorized into alpha-linolenic acid (ALA; perilla seed oil, nuts, etc.) that is mainly derived from plants and DHA, EPA (tuna, pacific saury, mackerel, etc.) that is animal-derived. Omega 6 includes linoleic acid (soybean oil, corn oil, etc.), gamma linolenic acid (borage oil, evening primrose oil, etc.), and arachidonic acid (liver oil, etc.). omega 9 includes oleic acid, the most common of which are olive oil and canola oil. When the chemical structure includes only one double bond, it is called monounsaturated fatty acid (MUFA) and when there are many double bonds, it is called polyunsaturated fatty acids (PUFA).
-To be continued
