Food and Feeding

Why do we need to eat?

Food contains the complex chemicals that every cell in our body needs to provide energy to support all the life processes such as growth, movement and repairing the body. Humans, like all other animals, cannot make their own food like plants do. Instead we have to get our food by eating plants, or by eating other animals.

As well as providing us with energy, our food also contains other nutrient and chemicals that our bodies need to function properly – such as fats, proteins, vitamins and other minerals.

Food Groups

The food that we eat can be divided up into different groups. There are a few different ways of doing this but one way to classify the different food groups is as follows:

• Starchy Foods (Bread/rice/pasta/potatoes)
• Milk and Dairy (milk, cheese, yoghurt)
  
• Fat and Sugar
  
• Protein (meat, fish, beans, eggs)
• Fruit and Vegetables

Remember – there’s no such thing as an unhealthy food, just unbalanced diets. A lettuce can be thought of as a “good” food, but if all you did is eat lettuce you’d end up sick with malnutrition. A healthy diet includes something from every group. Our bodies need fat and sugar too!

The Digestive System

Digestion is the process where the food we eat is broken down into smaller chemicals that can be absorbed and used by the body. It takes place in several stages.

First, food enters the body through the mouth, where it is chewed by the teeth and mixed with a liquid called saliva. Saliva contains special chemicals called enzymes which can be used to cut up big chemicals into smaller ones. Saliva contains the enzymes amylase and lipase, which begin to break down starch and fat respectively. Saliva also acts as a lubricant, making the food wet and soft enough to swallow easily. This lump of chewed food is called a bolus.

When it is ready to be swallowed, the food moves to the back of the throat where muscle contractions push it into the oesophagus. The oesophagus is a long tube that connects the mouth to the stomach. The muscular walls of the oesophagus contract and relax pushing the food downwards.

The stomach stores the ingested food and uses gastric juices to continue the digestive process. The walls of the stomach are wrinkled and folded, allowing it to expand as it fills. The stomach is lined with mucus to protect it from the strong digestive acids. Food can stay in the stomach for up to several hours before being pushed through the duodenum into the small intestine.

As the food passes through the small intestine enzymes are secreted into onto the food by glands in the intestine walls. Digestive juices are also produced by the gall bladder (bile) and pancreas. Slowly the food is broken down into small chemicals such as amino acids and glucose and these can then be absorbed through the lining of the small intestine into the bloodstream. The walls of the small intestine are highly folded to give it a large surface area for absorbing as quickly as possible. Water from our food and drink is also absorbed.

The absorbed chemicals are then transported via the bloodstream to the liver for processing and then sent around the body to be used.

Food that cannot be digested easily passes into the large intestine. This contains up to a thousand species of bacteria who feed off it creating useful vitamins and also also breaking down some of the fibre. The walls of the large intestine absorb these vitamins as well as water.

Poo is the waste that remains after food has been digested and its nutrients absorbed. The scientific word for poo is faeces. Poo contains water, fibre, bile and bacteria.

Useful Links

• Food: A fact of Life
• Zygote Body – see all the organs
• Food for Life
• Food in Schools
• Here’s a fun demonstration to model the function of the digestive system.
• Here’s another demonstration to investigate the iron in our food.

Glossary

Digestive system : The group of organs that work together to break down and process food into components that can be utilised in the body.

Saliva : A fluid produced in the mouth that contains enzymes that help digest food.

Oesophagus: A muscular tube that carries food from the mouth to the stomach.

Stomach: A  bag-shaped organ where acids and enzymes partially digest food.

Pancreas: Produces hormones and digestive juices that help the digestion and absorption of nutrients in the small intestine.

Liver: An organ that secretes bile and plays an important role in digestion, removing toxins from the blood and storing carbohydrates, vitamins and minerals in the body.  The liver is the largest organ inside the human body.

Small intestine: Responsible for digesting and absorbing nutrients and minerals from food.

Large Intestine: A part of the digestive system responsible for absorbing water from undigested food and passing waste products from the body.

Faeces: Waste material that cannot be absorbed by the body, plus fibre and dead bacteria, pass out of the body when we go to the toilet.