The Absorbed Food

The dissolved parts of the food are absorbed through the wall of the small intestine into the blood. These parts of the food are taken to all parts of the body to provide energy for growth and other activities.

Foods which give us Energy

Foods contain special chemicals which provide us with energy. 

Carbohydrates

Sugar is a carbohydrate. Sugar gives energy to our muscles to help us walk and run. It also gives energy to the brain. There is a lot of sugar in foods, such as chocolate, fruits and milk.

Starch is another carbohydrate. It does not taste sweet like sugar but is gives us as much energy. We find starch in all foods made from cereals, such as wheat. Cakes, bread, pasta and rice are full of starch.

Proteins

Proteins not only give us energy but are very important for growth. A young child should be given plenty of protein in its diet. Foods from animals are good sources of protein. Milk, meat, eggs and cheese supply a lot of protein. Some plant seeds also contain protein. Vegetarians have to include soya beans in their diet to make sure that they have enough protein.

Lipids

Solid lipids are called fats and liquid lipids are called oils. Both types of lipid contain a lot of energy. Many plant seeds contain oils; castor oil, sunflower oil and maize oil are just three examples. Eggs, cheese, meat and milk are animal foods which contain lipids.

To be healthy and to have lots of energy your diet must include foods which give you carbohydrates, protein and lipids. There are other important chemicals, however, which your body needs. 

Vitamins

Every day you need to eat foods which will give you vitamins. These chemicals are needed to make your body work properly. Fruits, such as oranges and lemons, give you a vitamin C. Fish is a good food to eat to get vitamin A. There are 14 different vitamins and you need a daily supply to keep healthy. People who are tired and look ill often take vitamin tablets, which usually help them feel better.

Vitamin A is found in foods such as liver and carrots. We need it for our eyes, so that we can see well in the dark. People who do not have enough vitamin A in their diet suffer from night blindness.

Vitamin B is a complex vitamin. Vitamin B₁ is found in yeast products and cereals. A lack of vitamin B₁ in the diet causes a skin disease called beri-beri. This disease is common in some parts of Africa where vitamin  B₁ is lacking in the diet.

Vitamin C is found in citrus fruits and green vegetables. 

A lack of vitamin C in the diet causes a disease called scurvy. The first symptoms of scurvy are bleeding gums and loose teeth.

A good source of vitamin D is fish liver oil. Once it is in the body, vitamin D goes to the skin where it is made 'active' by sunlight. A lack of vitamin D in the diet or a lack of sunlight can cause a disease called rickets. A person with this disease has soft and deformed bones.

Water and Roughage

Your body also needs chemicals which are called minerals to help it work properly. Iron is needed in the blood and calcium makes your bones strong. Salt is needed by the nerves and flouride makes your teeth strong. Most foods contain minerals which are absorbed into the body.

Water is also very important. We cannot live for very long without it. An adult human needs 1,5dm³ of water each day. Many foods contain water; some fruits are 95% water. In Europe we are lucky because there is usually plenty of water but in some countries, where there is not much rain, there is not enough water for the people who live there.

The parts of the food which we cannot breakdown and digest are still important to us. They help our gut to work properly. These parts of the food are called roughage or dietary fiber.

Energy in Foods

Most foods which are bought already packaged will have a list of the important chemicals they contain somewhere on the packaging. This list also tells you how much of a certain chemical is present either in one hundred grammes of the food or in the whole packet. Next time you go to the supermarket, look out for this information on the packaging of the foods you buy.

Usually the amount of energy which each chemical provides is also listed on the packaging of the food. Again, this is sometimes shown for one hundred grammes of the food or for the amount of food in the packet.

Energy is measured in calories or joules. The amount of energy is usually shown as both kilocalories (kcal) and kilojoules (kJ). One kilocalorie is equivalent to 4,2 kilojoules, so the number of kilocalories indicated on the packet is always less than the number of  kilojoules.

• How Food is Digested
• The Digestive Systems of Other Animals
• Chapter Summary (useful for revison)
• Questions relating to this chapter
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© Paul Billiet and Shirley Burchill 2008