All living organisms require food:

  1. for energy (for heat & to support chemical reactions & for continuity of life),
  2. to provide necessary building materials for growth, maintenance & repair of cells, and;
  3. to control chemical reactions in cells

A balanced diet should contain 2/3 carbohydrates (including roughage), 1/6 protein, 1/6 fat, minerals, vitamins & water.

Energy value of food:

  • 1 kcal = 4.2 kilojoules (kJ) .  
  • 1 kJ is the amount of energy required to increase the temperature of 1kg of water by 1oC. 
  • 1g carbohydrate = 16kJ of energy / 1g protein = 17 kJ/ 1g fat = 38 kJ/ 1g alcohol = 29kJ
  • The total amount of food intake depends on age (young people needing more than older individuals), level of activity, health and gender.  Males require more food than females because they have a higher muscle to fat ratio.  More intake is required during pregnancy - growth of foetus - and lactation - milk production.  The recommended allowance = 9600kJ for 16 year old girls and 12600 kJ for boys.  Moreover, it is important to reduce fat intake when trying to control weight.  Climate also plays a moderating role in kJ intake, with more kJ required in colder climates to maintain body temperature.


These are organic compounds made in living organisms, of which there are four types found in food, namely proteins, carbohydrates lipids and vitamins. Each of these are discussed in the subsections below.


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