Nutrients and Their Functions

Nutrient : A substance essential for the growth, maintenance, function and reproduction of a cell or organism. OR The essential substances contributed by food are called nutrients.

There are several categories of nutrients, includes carbohydrates, proteins, fats, vitamins, minerals and fibre. 

• The nutrients are classified into two categories: 

Macronutrients: Are those which the body requires in relatively large amounts. The requirement of these nutrients are in grams. Ex: Carbohydrates, fats and proteins. 

Micronutrients: Are required in much smaller quantities by the body. The requirement of these nutrients in milligrams and micrograms. Ex: Vitamins and minerals.

• Functions of Nutrients

Generally three major functions are performed by nutrients. These are,  

1. Supplying energy 
2. Building body tissues
3. Protecting the body from infection and regulating body processes

Each nutrient class has its own function. The nutrients found in foods are carbohydrates, proteins, fats, minerals, vitamins and water. Fabre is also an essential component of our diet. 

Carbohydrates: 

Starch found in cereals and sugar in sugarcane and fruits are examples of carbohydrates in foods.  The main function of carbohydrates is to provide energy needed by our body.  Those not used immediately for this purpose are stored as glycogen or converted to fat and stored and to be utilized for energy supply when needed. 

One gram of carbohydrate provides about 4 kilocalories (4 Kcal). Energy is measured in kilocalories.  One kilocalorie is the amount of heat required to raise the temperature of one kilogram of water by one degree centigrade.

Fats: 

Oils found in seeds, butter from milk and lard from meat, are examples of fats found in foods. Fats provide more than double the energy supplied by carbohydrates, 9 Kcal per gram. This makes them concentrated sources of energy. Foods rich in fat provide satiety and are more palatable. Fat which is not used by the body is stored by a specific tissue called adipose tissue. Adipose tissue is present under the skin and around vital organs and prevent excessive heat loss and keep the body warm.
One of the major functions of the fats is as sources of essential fatty acids. The unsaturated fatty acid cannot be synthesized by the body. The essential fatty acids called linoleic and linolenic acids. Fats are also important as a vehicle for carrying fat-soluble vitamins and also aid in their absorption.

Proteins: 

Casein from milk, albumin in egg, globulins in legumes and gluten in wheat are examples of proteins occurring in foods. About 10 per cent of the total energy is supplied by proteins in the diet. It provide 4 kilocalories/ gram. Protein taken in excess is converted to carbohydrates and fats and is stored in the body. The main function of protein is the building of new tissues and maintaining and repair of those already built. Synthesis of regulatory and protective substances such as enzymes, hormones and antibodies is also a function of food proteins. Protein also fulfil requirement of essential amino acid of human body. Examples are Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine. (Histidine And alanine essential only for  infants only).

Vitamins: These are needed for growth, normal function and processes of the body.

a) The water soluble vitamins:

Folic acid and vitamin B12 are important in formation of normal red blood cells in the bone marrow. The proper functioning of the digestive tract and nervous system also requires sufficient intake of vitamin B12 and B6 Vitamin C is another water-soluble vitamin. Its major functions include its role in collagen formation. Collagen is a protein and it forms a part of connective tissues. Proper synthesis of collagen helps wound healing. B-complex vitamins play a crucial role in the metabolism of carbohydrates, fats and proteins. Vitamins such as thiamin, riboflavin, niacin and folic acid are referred as coenzymes.