Most of the properties of fats depend on the length of the carbon chain and the degree of saturation in the molecule.
Fatty acids which are unsaturated and those saturated acid which have less than twelve carbon atoms are liquids at room temperature. Saturated fatty acid containing fourteen or more then fourteen carbon atoms is solid at room temperature.
Unsaturated fatty acid can be hydrogenated in the presence of nickel which acts as a catalyst. Vegetable ghee is made by the process of hydrogenation of unsaturated fatty acids.
Fat can be oxidized at room temperature causing changes in odour and flavor. When this occurs the fat turns rancid.
Excessive heating of fats can leads to the breakdown of glycerol which can harm the mucous membrane of the intestines. This is why foods cooked in repeatedly heated fats cause irritation to the throat and digestive tract.
Fats are richest source of energy. One gramme of fat gives 9 calories of energy which is more than double the amount obtained from equal amount of carbohydrates and protein. Any excess of energy in the body is stored in the body as fat. Adipose tissue which consists mainly of triglycerides is stored under the skin, around the organs and in the abdominal cavity.
The layer of just under the skin helps in maintaining the body temperature. Losses of body heat are prevented with the help of this subcutaneous layer of fat.
Vital organs like the kidneys have a thin layer of around them which protects them from shocks and physical injury.
Fats help in lubricating the gastrointestinal tract and a diet rich in fat has a higher satiety value.
Some of the fat soluble vitamins like A, D, E and K need fats for their proper utilization in the body .the body can suffer from deficiency of these vitamins if enough fat is not present in the diet.
Fats are obtained from vegetables as well as animal sources
Some seeds like mustard and sesame (til) are rich in oil which can be extracted from them. Nuts like peanuts coconut and almond also contain a considerable amount of fat.
Milk, egg yolk and animal fats like butter, suet and lard are some of the fats of animal origin.
It is difficult to make any statement about the amount of fat necessary in the diet. Some amount is necessary for the provision of essential fatty acids and absorption of fat soluble vitamins. A reasonable amount is desirable for the diet to have a satiety value. People living on diets vary low in fat, tend to feel hungry all the time. On the other hand excess fat generally reduces appetite. Most people are not able to easily digest meals too rich in fat. Since the caloric value of a diet is derived mainly from fat and carbohydrates, any drastic restriction in one means that the other must be increased in one means that the other must be increased in order to maintain the caloric equilibrium.
According to the balance diet studies by ICMR, 30%of the daily caloric needs are met by the fats. The Indian diet is cereal-legume based and the invisible fat content of these contributes about 9%of the energy needs. Reset calories are derived from the visible fats i.e., butter ghee and oil, consumed each day.