Classification of fats
Fats are classified into 4 categories as follows:
1. On the basis of chemical composition
2. On the basis of fatty acids
3. On the basis of requirement
4. On the basis of sources
Fats can be classified into 3 main groups as follows:
These are esters of fatty acids and glycerol. They are also called as neutral fats or triglycerides. These neutral fats make up 98 -99% of food and body fats.(e.g) fats and oils
Waxes: A wax is a simple lipid which is an ester of fatty acids and long chain aliphatic alcohols. The alcohol may contain 12-32 carbon atoms. Waxes are found in nature as coatings on leaves and stems. The wax prevents the plant from losing excessive amounts of water.
The compound lipids contain, in addition to fatty acids and glycerol,some other organic compounds.
1. Phospholipids: These contain phosphoric acid and a nitrogenous base in addition to fatty acids and glycerol(e.g.)Lecithin and cephalin
2. Glycolipids: Complex lipids containing carbohydrates in combination with fatty acids and glycerol(e.g) Cerebrosides
3. Lipoproteins: Lipoproteins are the most important as they are the carriers of lipids in the blood and form cell membranes.
3. Derived lipids
These are substances liberated during hydrolysis of simple and compound lipids which still retain the properties of lipids. The important members of this group are sterols, fatty acids and alcohol.
i. Sterols : Sterols are solid alcohols and form esters with fatty acids. In nature they occur in the free state in the form of esters. Based on their origin sterols are classified as cholesterol (animal origin) and phytosterol (in plants).
Cholesterol is a waxy, fat-like substance found in all cells of the body and has several important functions in the body. It is synthesized in the body by the liver independent of the dietary intake. The body normally synthesizes about 2 grams of cholesterol. The dietary sources of cholesterol includes animal foods. It is used in the body for synthesizing hormones, Vitamine D and substances which help digest foods. High blood cholesterol is a risk factor for heart disease. Rich sources of dietary cholesterol include meat, poultry(with skin), organ meats like brain, kidney, liver and full fat dairy products.
ii. Fatty acids: They are the key, refined fuel form of fat that the cell burns for energy. They are the basic structural unit of fats and they may be saturated or unsaturated. (e.g) Oleic acid, linoleic acid, linolenic acid, palmitic acid and myristic acid.
Fats can be classified based on the fatty acids present in them as follows:
A saturated fat is a type of fat in which the fatty acid chains have all or predominantly single bonds. Various fats contain different proportions of saturated fat.
Saturated fatty acids, especially palmitic and stearic acids are found in animal products such as cream, cheese, butter, other whole milk dairy products and fatty meats which also contain dietary cholesterol. Certain vegetable products have high saturated fat content, such as coconut oil and palm kernel oil. Many prepared foods are high in saturated fat content, such as pizza, dairy desserts and sausage.
An unsaturated fat is a fat or fatty acid in which there is at least one double bond within the fatty acid chain.
i. Monounsaturated fatty acid (MUFA): A fatty acid chain is monounsaturated if it contains one double bond. Monounsaturated fats are good fats. A diet high in MUFA can reduce blood cholesterol levels, lowers risk of heart disease, stroke and breast cancer, reduces pain in rheumatoid arthritis and helps in weight loss. Foods which contain MUFA (Oleic acid) are avocados, olives, olive oil, peanut butter and peanut oil. It is also known as omega-9 fatty acid.
(ii) Polyunsaturated fatty acid (PUFA): A fatty acid is polyunsaturated if it contains more than one double bond. They are of 2 types, namely Omega-3 and omega-6 fatty acids.
a. Omega-3: It is also called ω−3 fatty acids or n−3 fatty acids with a double bond (C=C) at the third carbon atom from the end of the carbon chain. The three types of omega−3 fatty acids involved in human physiology are α-linolenic acid (ALA) [found in plant oils], eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) [both commonly found in marine oils]. Common sources of plant oils containing the omega−3
ALA fatty acid include walnut, flaxseed, flaxseed oil,soybeans and chia seeds.The sources of animal omega−3 EPA and DHA fatty acids include fish and fish oils.
The health benefits of omega-3 fatty acids are immense and they have been proven effective in the treatment and prevention of hundreds of medical conditions which includes high cholesterol, depression, anxiety, cancer, diabetes mellitus, inflammatory diseases, arthritis and cardiovascular diseases.
b. Omega-6: Omega-6 fatty acids (also referred to as ω-6 fatty acids or n-6 fatty acids) are a family of pro- inflammatory and anti-inflammatory polyunsaturated fatty acids that have in common a final carbon-carbon double bond in the n-6 position, that is the sixth bond, counting from the methyl end.
Omega-6 fats, also known as linoleic acid, are available only in food. The human body cannot make them, so they are considered essential fats. They support brain function, bone health, reproductive health, hair growth and regulation of metabolism. Good sources of linoleic acid include vegetable oils.
Fatty acids are of 2 types:
Fatty acids which are essential to be taken in our diet because they cannot be synthesized in our body are known as essential fatty acids.(eg.) Linoleic, linolenic and arachidonic acids.
Non-essential fatty acids are those which can be synthesized by the body and which need not be supplied through the diet. Palmitic acid, oleic acid and butyric acid are examples of non– essential fatty acids.
Fats are divided into 2 types based on their source, namely visible and invisible fats. Some fats and oils added to food or used for frying are visible fats.
These are also known as pure fats. Many foods like milk, cream, egg yolk, meat, fish and even cereals and legumes contribute substantial amount of invisible fats (not visible in the food) to the diet.