Fats and oils are esters of triglycerides with three long chain carboxylic acids. They are classified under lipids. When they are hydrolyzed, they form glycerol and fatty acids. The main difference between fats and oils is that, fats are solids at room temperatures whereas, oils are liquids.
Lipids are water insoluble molecules that are composed of carbon and hydrogen. They are further classified into fats, oils, waxes, cholesterol and other steroids. The term lipids are often interchanged with fats.
Many of our dietary foods contain certain amounts of fats. Fats are stored in adipose tissue. Fats are important for maintaining healthy skin, and hair. Stored fats act as insulator for body temperature loss. When body is deprived of energy, body starts burning fats to release energy. In the nerve tissue, lipids present in myelin sheath around axons prevent damage and signal leakage. Fats are involved in cell membrane synthesis, formation of good and bad cholesterol, hormones and phospholipids. Fat soluble vitamins like vitamin A, D, E and K are absorbed in the presence of fats.
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Fats that are obtained from animal and plant sources differ widely in chemical structure and effect on the body. When fats are hydrolyzed, they give glycerol and fatty acids. The composition of fatty acids differs with various foods. Based on the fatty acids and their effect on health, fats are divided into saturated fats, unsaturated fats, polyunsaturated and trans fats.
Saturated fat (Bad fat)
Saturated fat contains mainly saturated fatty acids. Saturated fats are present in dairy products like whole milk, cheese, butter, sausages, cakes, chocolates and cookies. These fats increase the bad (LDL) cholesterol though reports say that they increase good (HDL) cholesterol as well. Research suggests that saturated fat containing foods cause heart diseases like atherosclerosis by blocking the blood vessels.
Trans fat (Bad fat)
Trans fats are made commercially by hydrogenating (addition of hydrogen) mono and poly unsaturated fatty acids. The purpose of this is to store the food for long time and make them attractive. During hydrogenation they become saturated fats and are of no nutrition value. Look for labels for trans fat. Partially hydrogenated oils, deeply fried chips and baked foods contain trans fat and cause high risk to health. Trans fats increase bad (LDL) cholesterol.
Mono and poly unsaturated Fat (Good Fat)
In general, unsaturated fats are good for health because they lower bad (LDL) cholesterol and increase good (HDL) cholesterol. Oleic acid is monounsaturated fatty acid. Corn, sunflower oil, olive oil, nuts, cotton seed, fish are some of the common sources of unsaturated fats.
Essential fatty acids are the fatty acids that must be obtained from the diet. They cannot be synthesized in the body. They are derived from linolenic, linoleic and oleic acids. There are two main types. Omega-3 fatty acids and Omega-6 fatty acids. They are needed for skin, hair and bone growth. They also regulate metabolism in the body. Poor supplement of these acids can cause skin and other infections and also delays in healing.
Omega-3 fatty acids
These are polyunsaturated fatty acids. Fish oil is the major source of Omega-3 fatty acids. They are present in soy oils, margarines, salmon fish, bluefin tuna. There are two main acids in Omega-3 fatty acids; eicosapentaenoic acid (EPA) and decosahexaenoic acid (DHA). EPA participates and prevents inflammation and pain and keeps platelets away from clotting the blood whereas DHA makes up cell wall and is also rich in brain.
Omega-6 fatty acids
These are mainly found in nuts, seeds, corn, soya. Omega-6 fatty acids have the opposite effect on platelets and clotting compared to Omega-3 fatty acids, although both are important for skin, hair and brain. These acids increase arachidonic acids and increase pain. Having high Omega-6 fatty acids to that of Omega-3 fatty acids could be of risk to heart because Omega-6 fatty acids show opposite effect and involves in platelet clotting.
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Lipids are water insoluble molecules that are composed of carbon and hydrogen. They are further classified into fats, oils, waxes, cholesterol and other steroids. The term lipids are often interchanged with fats.
Simple Lipids, compound lipids, steroids and terpenoids
Simple Lipids
Fats, oils and waxes come under simple lipids. Animal fats and vegetable oils are most widely occurring lipids. Chemically, fats and oils are esters of three fatty acids and glycerol. Fats are solids in room temperature and oils are liquids at room temperature. They differ in length and type of fatty acid.
Animal Fat e.g. butter, lard
Vegetable oils e.g. peanut oil, coconut oil, olive oil
Waxes are esters of ethylene glycol and two fatty acids. e.g. bees wax (from bees), Shellac (from lac insect), wool wax (sebaceous gland of sheep).
Compound lipids
Lipids that bind with other groups like phosphate, carbohydrate are called compound lipids.
Phospholipids
Two main kinds of phospholipids are phosphoglycerides and sphingolipids. Phosphoglycerides contain phosphoric acid along with fatty acids and glycerol whereas sphingolipids are derived from aliphatic amino alcohol spingosine. Phosphoglycerides are further divided into phosphatidylcholine (lecithins) and phosphatidylethanolamine (cephalins). Lecithins are building blocks of all cells and required by all cells. They are daily produced by liver. Lecithins are rich in egg yolk. They are also found in soya. Cephalins are especially found in white matter of brain and spinal cord.
Sphingolipids: Sphingolipids are present in nervous tissue and brain
Glycolipids are lipids that are attached to carbohydrate. These are further classified into cerebrosides (galactocerebrocites, glucocerebrocites), gangliosides, globosides, sulfatides, sulfolipids and proteolipids.
Steroids and terpenoids
Main Steroids are cholesterol and ergosterol. Cholesterol is rich in egg yolk. It is also found in dairy products and meat. Ergosterol converts into ergocalciferol (vitamin D) in the presence of ultraviolet light. Terpenoids are found in plant pigments and in essential oils. Vitamin A, E, K are related to terpenes.
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The lipid digestion solely takes place in small intestine. Lipids are broken down into glycerol and fatty acids by pancreatic enzyme called lipase. Lipase is released into duodenum, first part of small intestine. Lipase is a water soluble enzyme but lipids are water insoluble. In order to make available for lipase to breakdown the lipids, bile is secreted into duodenum from gall bladder. Bile is synthesized in liver and stored in gall bladder. Bile emulsifies lipids. Emulsification is a process of making bulk lipid into droplets in a aqueous medium so that lipase can easily attack and breakdown into fatty acids and glycerol. Once broken down fatty acids and glycerol are absorbed into blood from small intestine. Fatty acids are transported to adipose tissue and stored. Glycerol enters liver and converts glucose for energy production. When sufficient energy is not available, fatty acids from adipose tissue breakdown to produce energy and glycerol converts to glucose in the liver. Fatty acids cannot form glucose. What happens to cholesterol? Cholesterol is obtained in diet or synthesized by acetyl- CoA through HMG-CoA pathway. Low density lipoproteins (LDL) transport cholesterol to cell membranes whereas high density lipoproteins HDL transport cholesterol to liver for excretion. In the intestine, cholesterol is reabsorbed or excreted.
The amount of fats required daily depends on the calorie requirement of a person. However, approximately 20 to 35% of calories should come from fats and less than 7% should come from saturated fats.
Excess fat makes obese and obesity is the major problem of chronic diseases. Excess fat, especially saturated fats and trans fats increase bad cholesterol (LDL). Excess bad cholesterol is associated with atherosclerosis and heart disease. Cholesterol or excess fat is one of the major factors that are associated with heart attacks.
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