The food supplied to the body consists of various elements, such as proteins, fats, carbohydrates, vitamins, minerals and water. Most foods contain all these factors but in varying proportion. Proteins, facts and carbohydrates are often termed proximate principles.
Together with water they form the main bulk of food. The human body is built up from the six constituents, and has the following approximate composition:
Water 63 percent
Protein 17 percent
Fat 12 percent
Minerals 7 percent
Carbohydrates 1 percent
However, the main functions of food are: (i) provision of energy (ii) body building and repair and (iii) maintenance and regulation of tissue functions.
The protein foods are much more complex in character and all contain nitrogen, an element which is essential to life. Proteins contain carbon, hydrogen, oxygen, nitrogen and sulphur in varying amounts. Some proteins also contain phosphorus and iron, and occasionally other elements.
Proteins are needed by the body (i) For growth and development, (ii) For repair and maintenance and (iii) For synthesis of certain substances like the anti I bodies, enzymes and hormones. Proteins are used as a source of energy. Proteins play a major role in the maintenance of goo nutritional status. At present, protein malnutrition is the greatest threat to health especially among children.
Proteins are found in both animal and vegetable foods and are spoken of as animal and vegetable proteins. The animal sources of protein are milk, eggs, meet, fish, liver, etc. while vegetable proteins are found chiefly in the pulses such as dal, peas and beans. Modern nutritional scientists prefer to use the term 'protein rich foods in place of first or second class proteins. The protein rich foods of animal sources and plant sources are essential in human nutrition.
Fats are important items in the diets of people. They contain carbon, hydrogen and oxygen.
(i) Fats are concentrated and palatable sources of food energy. One gram of fat yields about 9 calories of energy.
(ii) Fats carry fat-soluble vitamins— A.D.E. and K
(iii) Fats provide 'essential fatty acids'. These are required by the body for growth and maintenance of the integrity of the skin.
(iv) Fats provide support for many organs in the body such as heart, kidney and intestine. Fat beneath the skin is insulation against cold.
Dietary fats are derived from two main sources:
(i) Animal Sources:
They are ghee, butter and fish oils. Animal fats have more saturated fatty acids than vegetables fats. They also contain vitamins A and D which are lacking in vegetable fats.
(ii) Vegetable sources:
They include various vegetable oils such as groundnut, mustard and coconut oil. Vanaspathi which is a popular cocking medium in India is manufactured from groundnut oil and cottonseed oil, which are converted into solid fat.
Fats such as butter, ghee and vegetable oils are known as 'visible' fats because it i= easy to estimate their intake. But fats present in such foods as milk, eggs, meat and .nuts which also find a place in the human diet are difficult to estimate and are therefore called 'invisible' fats.
Carbohydrates are the chief source of energy of the body. In most Indian diets, carbohydrates are present in excessive amounts, providing as much as 90 percent of the calories in some -cases. In balanced diets, carbohydrates provide not more than 50 to 60 percent of the total calories. The carbohydrate reserve of a human adult is only about 500g. When a man fasts, this reserve is rapidly exhausted.
There are three main sources of carbohydrate: (i) Starches, (ii) Sugar and (iii) Cellulose Starches are present in plenty in cereals, roots and tubes and also in plant stems. Cereals (wheat, rice) account for most of the dietary carbohydrate. Sugar can be found in fruits; honey and things that produce sugar. Glucose is an essential element of sugar. This is very much needed for small children, especially during the period of teething and their growth. Lactose and jams, other fruits and honey also provide sugar. The consumption of sugar increases as the economic status of the people rises. Cellulose is the fibrous substance of fruits and vegetables. It is hard to digest and has no nutritive value. Its main function is to serve as roughage and facilitate bowel movements.