All living organisms require food. Food has six types of nutrients - carbohydrates, proteins, fats, vitamins, minerals and water.

These are essential to perform all daily and metabolic activities.
Carbohydrates are compounds of carbon, hydrogen and oxygen, always in the ratio of 2:1:1.

  • They are oxidised in the cells to release energy. Carbohydrates include sugars, starch and cellulose.
  • Carbohydrates are oxidised in the body in the form of sugars. They provide instant energy.
  • When oxidised in the body, one mole of glucose releases 686 kilocalories of energy. 
  • They are mainly present in rice, potato, banana, etc.
Proteins are composed of carbon, hydrogen, oxygen and nitrogen.
  • Nitrogen is the most essential element in proteins. Some proteins contain sulphur and phosphorus.
  • Amino acids are the simple, smaller units of proteins. Proteins provide chemical material for the growth and repair of the body cells and tissues.
  • In an emergency, they may also oxidise to release energy. Food rich in proteins includes lean meat, fish, eggs, milk, cheese, nuts, beans, peas, etc.
Fats are also composed of carbon, hydrogen and oxygen. Fats have very little oxygen content, though..
  • They produce more energy than carbohydrates do.
  • Fat below the skin protects the body against rapid loss of heat.
  • It serves as a solvent for fat-soluble vitamins.
  • It is an important form for storage of food.
  • Common foods rich in fats are butter, cream, vegetable oils, meat, and fish liver oils.
Mineral salts are needed in the diet in small quantities. These are obtained from table salt, green vegetables and fruits.  Some important minerals are:   
Calcium, required for:

  • Strengthening bones and teeth
  • Blood clotting
  • Muscle contraction
  • Rich sources: Milk, meat, eggs, fish, pulses, vegetables, etc.
Phosphorus, required for:
  • Strengthening bones and teeth
  • For production of ATP in during cellular respiration
  • Conduction of nerve impulses
  • Rich sources: Milk, meat, eggs, fish, pulses, vegetables, etc.
Iron, required for:
  • Forming haemoglobin
  • Rich sources: Green leafy vegetables, liver, etc.
Iodine, required for:
  • Proper working of thyroid
  • Rich sources: Vegetables, mineral water and iodised salt
Vitamins are chemical substances that help maintain a healthy body.
  • Vitamins A, D, E, and K are fat soluble and can be stored in the body.
  • Vitamin B complex and vitamin C are water soluble and cannot be stored for a long period of time.
  • Vitamin A: Promotes growth, vision.
  • Present in butter, egg yolk, milk, carrot, etc.
  • Vitamin D: Helps the body to absorb calcium and phosphorus to form bones and teeth.
  • Present in fish liver oils, milk, eggs, etc.
  • Vitamin E: Prevents the oxidation of vitamin A.
  • Present in meat, milk, whole wheat, etc.
  • Vitamin K: Helps in clotting of blood during injuries.
  • Present in cabbage, spinach, leafy vegetables
  • Vitamin B complex:  Needed for a healthy brain, nerves and muscles.
  • Present in wheat, rice and liver.
  • Vitamin C:  Helps fight diseases like the common cold.
  • Present in oranges, tomatoes, lemons and guavas.
Water: Helps the body to get rid of toxic wastes through urine and sweat, and to absorb the
nutrients in food.

Balanced diet: The diet that contains all the principle constituents of food in proper quantity.

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