Without insulin the body cannot make full use of food that is eaten. Normally, food is eaten, taken into the body and broken down into simple chemicals, such as glucose, which provide fuel for all the activities of the body. These simple chemicals also provide building blocks for growth or replacing worn-out parts, and any extra is stored for later use. In diabetes, food is broken down as normal but, because of the shortage of insulin or because insulin does not work properly, excess glucose is not stored and builds up in the bloodstream, spilling over into the urine. Insulin ensures that a perfect balance is kept between the production of glucose by the liver and its use. The breakdown of food takes place in the liver, which can be regarded as a food processing factory. Glucose is one of the simple chemicals made in the liver from all carbohydrate foods. In the absence of insulin, glucose pours out of the liver into the bloodstream. Insulin switches off this outpouring of glucose from the liver and causes glucose to be stored in the liver as starch or glycogen. Insulin also helps glucose to get into cells where it is used as a fuel. Insulin has a similar regulatory effect on amino acids and fatty acids, which are the breakdown products of protein and fat respectively.

In people without diabetes, insulin is stored in the pancreas and released into the blood as soon as the blood glucose level starts to rise after eating. Insulin is released straight into the liver where it has the important role of regulating glucose production and promoting the storage of glucose as glycogen. The level of glucose in the blood then falls and, as it does so, insulin production is switched off (see Figure 1.2). Thus people who do not have diabetes have a very sensitive system for keeping the amount of glucose in the blood at a steady level. In diabetes this system is faulty. People with Type 2 diabetes can still produce some insulin but not in adequate amounts to keep the blood glucose level normal. This is because their insulin does not work properly (a condition called ‘insulin resistance’). People with Type 1 diabetes have little or no insulin of their own and need injections of insulin to try to keep the blood glucose level normal. Even if given four or five times a day, an injection of insulin is not as efficient at regulating blood glucose as the pancreas, which responds to small changes in blood glucose by switching the insulin supply on or off at a moment’s notice.
There are three main factors affecting your blood glucose:

• Food (which puts it up)
• Insulin
• Exercise (which both bring it down).

Any form of stress, in particular an illness like ’flu, puts up your blood glucose. Learning how to balance your blood glucose level is a matter of trial and error. This involves taking a lot of measurements and discovering how various foods and forms of exercise affect your blood glucose. In the past, people with Type 1 diabetes were brought into hospital to be ‘stabilized’ on a certain dose of insulin. Experience has shown that the insulin needed in the artificial surroundings of a hospital ward bears little relation to the amount needed in someone leading an active life in the outside world. Nowadays, you can ‘stabilize’ your own diabetes at home yourself.