What is fat

Lipids are a large class of compounds, which include fats, oils, waxes and a variety of other compounds such as cholesterol, phospholipids and lipoproteins. Their common properties are insolubility in water, solubility in organic solvents and usability by living organisms. Fats can be defined in three different ways. Commonly, a fat is anything, which is oily to the touch and not soluble in water. Chemically, fats are fatty acids, mostly in the form of triglycerides, but also found as monoglycerides, diglycerides, triacylglycerols and free fatty acids. For nutritional purposes, fats also include certain other lipids, which are nutritionally important. These include compound lipids, such as phospholipids and glycolipids; sterols, such as cholesterol; and synthetic lipids, which include medium-chain triglycerides, structured lipids and fat substitutes.

Fats supply more energy than carbohydrates because they contain proportionately more combustible carbon and hydrogen. Fats are the reverse fuel of the animal kingdom, supplying 9 kcal (38 kj) per gram, which is more than twice the energy per gram of proteins or carbohydrates. The fatty acids and triglycerides provide energy. Cholesterol usually forms cell membrane, and serves as base for the formation of hormones (cortisol, estradiol, testosterone).Fats also provide fat-soluble vitamins A, D, E, and K; impart flavor to food; and remain longer in the stomach than other foods, thus producing a sense of satiety. A high-fat diet is suitable for manual workers who require food with high calorie content but of reasonable bulk. Accumulation of fat is presumed to be storage for extra energy, but it has other functions like insulation and storage of vitamin A (beta carotene), vitamin E, and essential fatty acids.

Types of fat

Fats are an important part of a healthy balanced diet, and also act as a means of insulation in our bodies when it is stored under the skin as stored energy. Fats can be classified into different categories:

Saturated Fatty Acids

These are usually solid at room temperature. The do not have any double bonds and hence cannot combine with halogens or hydrogen. The common saturated fatty acids are palmitic, stearic, lauric and myristic acids. Palmitic acid is the most widely distributed and constitutes about 25%-30% of the depot fat of animals like sheep. Stearic acid is present in higher proportion in beef tallow and lard. Lauric acid and myristic acid are present in vegetable oils, particularly coconut and palm oils.

Unsaturated Fatty Acids

These can be classified according to the number of double bonds, as shown below.

• One double bond – oleic acid
• Two double bonds – linoleic acid
• Three double bonds – linolenic acid
• Four double bonds – arachidonic acid

Unsaturated fatty acids are usually liquid at room temperature. They are present in marine oils (whale, shark, etc) and vegetable oils (except coconut and palm oils, which have a preponderance of saturated fatty acids).

Monounsaturated fatty acids (MUFA): Diet high in MUFA is very useful in restoring the cholesterol levels. It also reduces the tendency of fat deposition in vessels as well as tendency of blood clot formation. Rich sources of MUFA are olive, canola oil.

Polyunsaturated fatty acids (PUFA) cannot be synthesized by humans and are obtained entirely from dietThere are two main classes of PUFA; these cannot be interconverted. The n-6 class includes linoleic acid, derived primarily from plant oil such as corn, safflower, soybean and sunflower oil. The n-3 class includes linolenic acid derived from plants and long-chain fatty acids obtained primarily from fish oils.