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Fats

 

 

 

 

 

 

 

 

Classification
Fats or Lipids are concentrated source of energy. They include fats and oils and fat like substances that have a greasy feeling and are insoluble in water but soluble in organic solvents like ether, benzene and chloroform. The main constituents of lipids are fatty acids.

Fatty acids can be either saturated or unsaturated.

Lipids can be classified as Simple lipids, Compound lipids and Derived lipids.

Simple lipids: are esters of fatty acids and glycerol (alcohol with three carbons and three -OH groups). They are further classified as:

Monoglycerides: formed by esterification of fatty acid with one -OH group.

Diglycerides: formed by esterification with two -OH groups

Triglycerides: formed by esterification with three -OH groups. They are also called as neutral fats. When the three fatty acids that are esterified are the same then they are known as simple triglycerides and when at least two fatty acids are different then they are called mixed triglycerides.

Compound lipids: are esters of fatty acids and glycerol and also other compounds such as phosphates, carbohydrates and nitrogenous groups.

E.g. Phospholipids, Glycolipids and Lipoproteins.

Derived lipids: are obtained when compound and simple fats are hydrolysed and they include fatty acids, glycerol and the fat soluble vitamins A, D, E and K.

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Food sources
On an average about three fifth of the fat is in the form of invisible fat which is naturally present in foods like meat, certain fish, poultry, eggs and dairy products except butter. Visible fats are butter, ghee (clarified butter), margarine, and oil. Vegetable oils, which are normally liquid at room temperature, are rich sources of PUFA (polyunsaturated fatty acid)

Meat, fish and poultry vary in their fat content. Fish have slightly lower content of fat than meat. Fat in egg is found in the yolk. Whole milk, cream, ice cream, cheese of whole milk provides appreciable amounts of fats. Fruits, vegetables, legumes and cereals are low in fat. Nuts have high amount of fat. Dietary sources of cholesterol are animal foods like liver, egg yolk, kidney and brain. Small concentration of cholesterol is found in whole milk, cream, butter, cheese and meat.

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Functions
Like carbohydrates, the primary function of fats is also energy. 1GM of fat, on oxidation gives 9 Kcal of energy. They are dense, insoluble and stored in the adipose tissues.

The sub cutaneous layer of fat is an effective insulator, reduces the loss of heat from the body in the cold weather. Vital organs like the kidney are protected against physical injury by a padding of fat.

Fats inhibit gastric secretion, thus delaying gastric emptying and therefore giving a feeling of satiety.

Fats act as carriers of fat-soluble vitamins - A, D, E and K.

Essential Fatty Acids or EFA are constituent of Phospholipids. They are an important part of the cell membrane and therefore have a role in cell permeability. They are also involved in the transport of lipids.

Phospholipids are widely distributed in the liver, brain and nervous tissue. They are important for nervous stimulation.

Fats are present in high concentration in the liver and adrenal glands, white and grey mater of the brain and the peripheral nerves. It is synthesized in the liver and is an important fraction of the blood. Cholesterol is a precursor of vitamin D. It's also required for the synthesis of adreno cortical hormones and steroid sex hormones and bile salts.

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Recommended Dietary Allowance (RDA)
In the Indian diet, fats provide 10-15 % of the total calories. 9% of the total fat energy is provided by invisible fat while the rest is provided by visible fat.

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