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Topic last updated: 25 Oct 2021

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Diet and digestion

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Food and digestion

The cells of your body need a regular supply of glucose. This is broken down in respiration to provide the energy needed for all of the chemical reactions in your cells. They also need the chemical building blocks of all the complicated molecules that go to make up the individual cells, the tissues and the organs of the body.

Plants are producers - they make their own food by photosynthesis. However we are consumers - we have to eat everything we need. The food we take in has to supply everything that our bodies use.

It doesn't matter what food you eat as long as it contains all of the ingredients your body needs to survive.

Why do you need to digest your food?

Imagine an apple, naan bread or a roast chicken. All of them are good to eat - but none of them are any use to your body unless they are broken down. Your body needs small soluble molecules such as glucose that can cross from inside your digestive system into your bloodstream by diffusion.

The food you eat gets into your body in big chunks which contain large, insoluble molecules. So to get the food you eat into a form that your body can use it must be digested. In your digestive system the food will undergo both physical digestion and chemical digestion.

  • Physical digestion is the physical breakup of your food; chopping it into small pieces with your teeth as you chew.
  • Chemical digestion is the chemical breakdown of the food molecules as they pass through the digestive system. This is largely a result of enzyme action.

The process of digestion takes place as the food passes along your digestive system or gut. This is a muscular tube which measures around nine metres from your mouth to your anus. The digestive process involves a number of stages:

  1. Ingestion - eating, taking food into your mouth
  2. Digestion - breaking down the large insoluble food molecules into small soluble molecules
  3. Absorption - taking the soluble food molecules into the bloodstream
  4. Egestion - getting rid of any undigested food from the body in the form of faeces

Food is more than a way of refuelling and restocking the body.

In human societies all over the world people share food within the family at mealtimes and use food as part of the celebrations of all the major events in life.

The basic sense of hunger is the result of a feedback mechanism between the hypothalamus in the brain and receptors in the body which supply information on the blood sugar levels and the amount of food in the stomach. If the blood sugar levels are low and the stomach is empty, we feel hungry and eat. If the blood sugar levels are high and the stomach is full, we do not feel hungry and don't eat.

However humans do not always eat just because they are hungry. When we eat more food than our bodies need, the excess is stored as body fat. This can lead to problems of obesity which in turn can lead to a number of health problems including cardiovascular disease and type 2 diabetes.

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