Constituents of Food: Carbohydrates, Proteins, Fats, Vitamins

Constituents of Food: Important Facts

Food is a nutritive substance taken by an organism for growth, work, repair, and maintaining life processes.

Functions of Food:

  • It provides energy to carry out the various life processes of the body.
  • It helps in the growth and repair of worn-out tissues.
  • It regulates the life processes and protects the body against diseases.

Constituents of Food:


  • Carbohydrates are the chief source of energy in our diet.
  • They are chemical compounds containing carbon, hydrogen, and oxygen.
  • Chief Sources of Carbohydrates are rice, wheat, maize, barley, potato, sugarcane, beetroot, banana, etc.
  • The carbohydrates produce energy when they are oxidized in the body.
  • The energy released by a foodstuff on oxidation can be measured in calories.
  • A calorie is defined as the amount of heat required to raise the temperature of one gram of water by 1°C.
  • One gram of carbohydrate provides about 4 calories of energy.
  • There are three types of carbohydrates in the foods that we eat. These are Cellulose, Starch, and Sugar.
  • Sugars are called simple carbohydrates.
  • They provide instant energy.
  • Sugar is present in milk and fruits like grapes, banana, sugarcane, and beetroot.
  • Starch and cellulose are complex carbohydrates.
  • Starch is the main carbohydrate in our diet since it is present in cereals which form the major part of our diet.
  • The main food like rice, chapati, and bread in our diet is called staple food.
  • A starch molecule is made up of many sugar molecules chemically bound to each other.
  • The sugar units are called monomers.
  • Many monomers join each other to form larger molecules called polymers.
  • Starch is one such polymer which is made from sugar monomers.
  • Cellulose is present in all cell walls.
  • Fruits and vegetables contain plenty of cellulose.
  • However, human beings cannot digest cellulose.
  • Cellulose thus forms the fibrous component of food and is called roughage.
  • Roughage helps in retaining water in the body.
  • Roughage adds bulk to the food and prevents constipation.
Carbohydrate Deficiency:
  • A diet deficient in carbohydrates leads to weakness in a person and loss of stamina.
  • Taking too much of carbohydrates can result in obesity. The excess carbohydrates are converted into fats and stored in the body.


  • Proteins are body-building food.
  • They are essential for the growth and repair of the body tissues.
  • Proteins are made up of amino acids.
  • Proteins are formed by different combinations of twenty amino acids.
  • Each amino acid contains carbon, nitrogen, hydrogen, and oxygen.
  • Some proteins contain elements like sulphur, phosphorus, and iron as well.
  • Enzyme Proteins– Pepsin and Trypsin.
  • Protein Hormone– Insulin.
  • Transport Proteins– Haemoglobin.
  • Contractile Proteins– Myosin and Actin.
  • Structural Proteins– Collagen.
  • Protective Proteins– Gamma Globulins which is present in the blood.
  • Muscles, skin, hair, and nails are made of proteins.
  • Wool and fur of sheep, lamb, and bear, and silk produced by silkworm are chemically proteins.
  • Enzymes are chemical substances that take part in several chemical reactions. Enzymes are chemically proteins. For example, salivary amylase is an enzyme produced by our salivary glands that break down starch into sugar.
  • One gram of protein when burnt yields about 4 calories.
  • Proteins can be classified into two groups-
  1. Animal proteins are obtained from animal products like milk, cheese, egg, fish, or meat.
  2. Vegetable proteins are obtained from plants like pulses, soybeans, nuts like cashew nuts, groundnuts, grains like barley, etc.
Functions of Proteins:
  • The fibrous proteins like keratin form the protective constituents of hair, skin, nails, horns, feathers, and wool. The silkworm cocoon is also made up of protein, fibroin.
  • Most of the proteins act as enzymes to catalyze the biochemical reactions and to control the metabolism.
  • Some proteins act as carriers to transport substances to different parts of the body. Hemoglobin transports the oxygen in the blood. Myoglobin of muscles stores oxygen. P-protein in plants transports organic food through the phloem.
  • Many proteins function as antibodies to provide defence mechanism to the body.
  • Many proteins function as receptor molecules that bind to specific information molecules like hormones to bring about cellular effects.
  • Actin and myosin are the contractile proteins that bind to specific information molecules like hormones to bring about cellular effects.
  • Some hormones like insulin and parathyroid are proteinaceous in nature which regulate the metabolism and other functions of the body.
  • Some proteins are storage in their functions like casein (milk), glutelin (cereals), and ovalbumin (egg white).
  • Proteins like fibrinogen and thrombin help in the clotting of blood.
Protein-Energy Malnutrition (PEM):

Protein-energy malnutrition is the most important nutritional disorder which affects the children in our country in the age group of 1 to 5 years.

PEM causes two diseases- Kwashiorkor and Marasmus.

  • Kwashiorkor is a disease caused by protein deficiency in children of 1 to 5 years age.
  • These children have swollen bellies, bulging eyes, thin legs, and their skin becomes scaly and develops cracks.
  • Kwashiorkor can be cured by giving a protein-rich diet to the child like a diet rich in animal protein or a diet containing wheat, gram, soybean, peanuts, and jaggery (gur).
  • Marasmus is a malnutrition disease which occurs due to the deficiency of proteins, carbohydrates, and fats in the diet of the small children (infants).
  • Marasmus occurs in infants (small children) of up to one year of age.
  • A child suffering from Marasmus becomes so thin that loose folds of skin can be seen all over the body.


  • Fats are esters of long-chain fatty acids and alcohol called glycerol.
  • The fats provide more energy than carbohydrates because fat molecules contain a higher percentage of carbon and hydrogen but less percentage of oxygen than that of carbohydrates.
  • Fat is mainly stored under the skin and protects internal body organs from jerks and shocks.
  • Fat helps in the absorption of vitamins A, D, E, and K as these vitamins are soluble in fats.
  • The major fatty acid present in butter is butyric acid.
  • The major fatty acid present in coconut oil is octanoic acid.
Functions of Fats:
  • It provides energy to our body as it is a high calorific value compound.
  • It is stored in our body as adipose tissue and provides energy under special needs.
  • It is an efficient insulator against cold.
  • It is deposited beneath the skin and it forms the shock-absorbing pads against any mechanical impacts.
  • Various vitamins like A, D, E, and K are soluble in fats and thus, fats help in their absorption in the body.
  • They provide energy to the developing embryo because fats stored in the seeds of groundnut, mustard, and castor, etc. can be easily converted to carbohydrates.
  • The edible oils extracted from the seeds of some plants are used for cooking purposes.
  • Waxes form the insoluble protective coating on the animal fur.
  • Sterols serve as a precursor for the synthesis of steroid hormones, vitamin D, and bile salts.


  • Vitamins are protective foods that are necessary for the well-being of the body.
  • Vitamins do not provide energy like carbohydrates and fats. They are therefore required in very small quantities and are essential for proper utilization of carbohydrates, fats, proteins, and minerals in the body.
  • Water-soluble vitamins are– Vitamin B-Complex (B1, B2, B4, Folic Acid, B12), and Vitamin C.
  • Fat-soluble vitamins (or Oil-soluble vitamins) are– Vitamin A, Vitamin D, Vitamin E, and Vitamin K.
Vitamins Function:
  • Vitamin A is necessary for maintaining healthy eye-sight (especially the night vision), normal skin, and hair.
  • Vitamin B1 is essential for growth, carbohydrate metabolism, the functioning of the heart, nerves, and muscles.
  • Vitamin B2 is necessary to keep skin and mouth healthy. It also helps in the normal functioning of the eye.
  • Vitamin B3 is essential for maintaining healthy skin, a good digestive tract, and sound mental health.
  • Folic acid is necessary for the formation and maturation of Red Blood Cells in the human body.
  • Vitamin B12 is necessary for the formation of healthy blood and proper growth of the body.
  • Vitamin C is necessary for keeping teeth, gums, and joints healthy. Also, help to resist infections.
  • Vitamin D is necessary for the normal growth of bones and teeth because it increases the absorption of calcium and phosphorous into the body.
  • Vitamin E is necessary for normal reproduction, normal functioning of muscles, and protection of the liver.
  • Vitamin K is necessary for the normal clotting of blood and prevents haemorrhage. It is also essential for the normal functioning of liver.
Vitamins Deficiency:
Vitamin A (Retinol):
  • Night blindness, poor vision, poor growth, abnormal bone, and teeth development.
Vitamin B1 (Thiamine):
  • A disease called Beri-Beri, extreme weakness, loss of appetite.
Vitamin B2 (Riboflavin):
  • Deficiency cause ariboflavinosis, Cheilosis (Inflammation and sometimes cracking at corners of the mouth), retarded growth, skin disease, loss of hair, premature ageing.
Vitamin B3 (Niacin):
  • Deficiency cause pellagra.
Vitamin B12 (Cynocobalamin):
  • Pernicious Anaemia (blood deficient in RBCs), digestive disorders, nervous disorders.
Vitamin C (Ascorbic Acid):
  • Deficiency cause scurvy.
Vitamin D (Calciferol):
  • Deficiency cause rickets in children- bending of bones, Osteomalacia (softening of bones in adults).
Vitamin E (Tocopherol):
  • Cause Anaemia.
Vitamin K (Phylloquinone):
  • Delayed blood clotting leading to excessive bleeding.



  • Functions- Formation of strong bones and teeth, blood clotting, muscle contraction.
  • Deficiency- Brittle bones, excessive bleeding, poor muscle movement.


  • Functions- Formation of strong bones and teeth, a component of the energy currency of cells.
  • Deficiency- Body weakness, bad bones, and teeth.


  • Functions- Formation of haemoglobin, the oxygen-carrying pigment present in Red Blood Cells.
  • DeficiencyAnaemia (blood deficient in RBCs).


  • Functions- Proper functioning of the thyroid gland.
  • Deficiency- A disease called goitre involving swelling of the thyroid gland.

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