Digestion, Food and diet:
what happens during exercise        Heart Disease

  • Food enters the body at the mouth
  • The food that we eat contains lots of nutrients.
    Nutrients are useful chemicals needed by our body.
  • In order to release the nutrients from the food the food needs to be broken down into smaller pieces.
    This breaking down of food is called digestion. and is helped by special chemicals called enzymes.
  • Digestion starts in the mouth.
    Our saliva contains an enzyme called amylase which turns cooked starch into sugar
  • After the food is digested the nutrients are absorbed into the blood
  • Most digestion takes place in the small intestine.
  • Unwanted food is removed from the body through the anus.


A diet is the type food we eat.

A balanced diet is selecting sensible foods so we have the right proportion of all the nutrients we need.

The table below shows the nutrients that need to be present in a balanced diet

Nutrient Why the nutrient is needed Example foods
Carbohydrate The main source of ENERGY for movement, warmth, cell repair, growth Sugar and starch eg potato, bread,
Fat Energy. Easier for our body to store than carbohydrate. Helps insulate the body from cold. Dairy food (milk, cheese), oils
Protein Body building. eg muscle growth, Repairing and building cells. Meat, soya, cheese
Vitamins Needed in small amounts to keep our body healthyeg Carrot (vit A) Marmite, bread (vit .B), Fresh fruit (vit C) Liver (vit D), Green veg. (vit.E).Vitamin. C helps stop a disease called scurvy Fresh fruit and vegetables.
Minerals Needed to keep us healthy eg calcium (strong bones): a lack of calcium can cause rickets.iron (making blood): a lack of iron can cause anaemia Milk and cheese (calcium); vegetables (eg spinach is rich in iron)
Dietary fibre* Helps digestion. Helps reduce the risk of heart disease by lowering cholesterol. Brown bread, vegetables, cereal
Water* Water is the main part of all living cells. Our body is 75% water. drinks , fruit

* strictly speaking water and fibre are NOT nutrients.

Fibre helps us to digest food .

We lose water all the time (eg by sweating and breathing out water vapour) and it needs to be replaced. A lack of water will make us ill far quicker than lack of food.

Milk is an important food as it contains most nutrients. It is rich in calcium so is an important food for growing children, however it does not provide a balanced diet. Other foods are needed to provide those nutrients not in milk.

Heart disease

Heart disease can be caused by too much fat which clogs the arteries reducing the flow of blood to the heart. Exercise helps reduce the risk by speeding the flow up blood up which helps clear the arteries.

How to help reduce the risk of heart disease:

  • Take regular exercise
  • Eat a balanced diet that is low in fatty foods
  • Don’t smoke (smoking can damage the arteries)
  • Avoid too much alcohol

What happens to the food I eat?
The food we eat is turned into energy by a special process called respiration

Resiration is a process carried out by every living cell in our body.
The energy is released from sugar, producing carbon dioxide gas as a waste gas.

Word equation for respiration:
Glucose + oxygen → carbon dioxide + water

Showing that our body is producing carbon dioxide

The aparatus is set up as below with a tube connected to the pipe marked ‘Mouthpiece’.
Tues A and B each contain limewater, a liquid that turns milky when carbon dioxide is bubbled through it. (this is the test for carbon dioxide).

When we breath IN air is drawn in through tube A.
When we breath OUT the exhaled air leaves through tube .

Which tube do you think goes milky first? Or do they both go milky at the same time?
Move your mouse here for the answer

What is the energy for?

The energy gets used by our body in several ways:

  •  Movement
  • Warmth
  • Growth
  •  Repair of cells

What happens when we run

Our muscles move more and so need more food and oxygen from the blood.

This causes the following changes in our body:

  • Our heart pumps quicker to get the blood to the muscles quicker.
  • We breath faster to transfer more oxygen to the blood
  • We sweat more. As the sweat evaporates it helps cool the body and remove excess heat.

How much energy does my body use?

Energy is measured in joules (1 joule of energy is needed to lift 1kg to a height of 1 metre)

A 12 year old boy will use about 12000 joules (3000 calories) a day
(1 calorie = 4.2 Joules)


For more information on food and energy see these links:

http://www.caloriecounting.co.uk/resources/intro.htm   Show the number of calories in different food types

http://www.exrx.net/Calculators/CalRequire.html   Show the number of calories needed for different activities