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Depot fat is not identical with food fat. With the customary diet, the depot fat of each species is a characteristic one. But if diet be altered in either quality or quantity specially after starving the animal, the depot fats may resemble food fat to a varying extent.
On the whole, depot fats are more unsaturated than food fats. One interesting fact about the depot fat is that, they are more unsaturated under the skin that in the deeper parts. The iodine value is found to diminish gradually from outside inwards.
Experiments with deuterium-labelled fatty acids indicate that fat depots are not static storehouses. They are dynamic. The stored fats are constantly being mobilised and replenished and in this way a dynamic equilibrium is maintained.
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About 12% of the total body weight of a man consists of fat. The major part of it remains stored in the so-called fat depots. This fat is called the depot fats.
The distribution of fat, in different fat depots, varies. For instance, subcutaneous tissue contains 50%, the perirenal tissue 15%, mesentery 20%, omentum 10%, the intramuscular connective tissue about 5% fat, etc. (average). These are the intracellular fats which remain inside the cell soft adipose tissue.
Depot fats are chiefly composed of the glycerides of various fatty acids and usually contain 75% of oleic acid, 20% of palmitic acid and 5% of stearic acid. They remain as mixed triglycerides, that is, one glycerol molecule is attached to three fatty acid molecules of either similar or dissimilar varieties. Traces of lecithin and cholesterol, as well as a little amount of polyunsaturated fatty acids, are also present.
The depot fats may be derived from the following sources:
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i. Food Fat:
This is the chief source
ii. Carbohydrates:
Carbohydrates of food may be easily converted into fats. Young pigs deposit large amount of fat only on a barley diet. During this conversion an oxygen-rich substance (carbohydrate) is being Trans formed into oxygen-poor substance, so that R.Q. rise. Fats formed from carbohydrates are more saturated and have a higher melting point.
Hence, depot fats of grazing animals are ‘hard’. This is of great importance in cattle farming.
iii. Proteins:
Recently, evidence shows that carbohydrates derived from protein may be converted into fats. It has been further shown that pyridoxine, in collaboration of thiamine, catalises the formation of fats from protein.
Some of the functions of depot fats are as follows:
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i. Mechanical Functions:
(a) While remaining under the surface, it gives shape to the limbs and body,
(b) Remaining around the viscera it keeps them in position and acts as a mechanical buffer against injury.
ii. Physical Functions:
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Fat being a non-conductor of heat, the subcutaneous fat plays a good part in the regulation of body temperature.
iii. Chemical Functions:
It represents stored energy. Large amount of energy can be stored as adipose tissue fat in concentrated water-free state. I gm of fat gives 9.3 Calories. Since fats constitute about 12% of body weight, it represents stored energy to the extent of 1,100 C per Kgm of body weight.
