The name diabetes comes from a Greek word meaning siphon and is so called because all types of diabetes have one thing in common and that is polyuria or passing abnormally large volumes of urine. There are two main classes of diabetes. Firstly, diabetes insipidus and then the other main type is diabetes mellitus.

Diabetes insipidus is rare whilst diabetes mellitus, which is the diabetes that we all talk about, is now very common and becoming increasingly so. Diabetes mellitus is further divided into two types which we refer to as type 1 diabetes and type 2 diabetes. Type 2 diabetes is associated almost exclusively with obesity for reasons that we’ll come on to shortly.

Diabetes was first recognised by Greek physicians who made a distinction between diabetes insipidus and diabetes mellitus based on how the urine tasted. In fact, they used a small tasting spoon to sample the patient’s urine. The urine in a patient with diabetes insipidus tasted as the name suggests – insipid. Whereas the urine in patients with diabetes mellitus (mellitus means honey) was sweet due to the sugar content.

Diabetes insipidus is due to a lack of a hormone called vasopressin, or antidiuretic hormone (ADH) which is produced by the pituitary gland and carefully regulates the body’s state of hydration by having a direct effect on the kidney.

There are two main causes – either a benign tumour of the pituitary gland, effectively preventing the secretion of the hormone into the blood. The other main cause is trauma to the brain resulting in once again damage to the pituitary gland and failure to release vasopressin into the blood stream.

The effect of vasopressin on the kidney is to reabsorb most of the water that is filtered by the kidney and therefore a lack of this hormone results in an excessive amount of water appearing in the patients’ urine. The end result is the passage of huge volumes of urine and there is at significant risk of becoming severely dehydrated as a result.

The other type of diabetes, namely diabetes mellitus, is due to a failure of the body to control the amount of glucose in the blood. Under normal circumstances blood glucose is maintained within fairly strict parameters i.e. 4.4 to 6.1 mmol/l. If it rises beyond this normal range, it fails to get filtered by the kidney and appears in the urine. This has an osmotic effect on the water in the kidney, effectively drawing it out and once again producing larger volumes of urine.

As previously mentioned, there are two types of diabetes mellitus and the underlying problem with both types is related to insulin. Insulin is the hormone secreted by the pancreas and is directly responsible for maintaining blood glucose within its strict parameters. In type 1 diabetes there is insufficient insulin and in type 2 diabetes there is too much insulin.

Type 1 diabetes is an auto immune disease in which the cells that produce insulin are destroyed by the patient’s own body for reasons that are not clear, resulting in a failure of the pancreas to produce sufficient amounts of insulin in response to a rise in blood glucose.

The other type of diabetes mellitus is type 2 diabetes where there is an increased resistance to insulin. In this condition there is, in effect, too much insulin, the commonest cause of which is obesity.

When an individual takes in food, in particular carbohydrate, this is absorbed in the form of glucose and the body’s automatic response to a rise in blood glucose is for the pancreas to produce insulin. This has the effect of pushing glucose into the cells for utilisation as energy or, if not utilised straight away, into adipose tissue.

Once the blood glucose level has fallen, insulin levels effectively return to zero quite quickly. However, if another meal is taken in fairly soon after this then once again the insulin levels will rise and if this continues on a regular basis then effectively the insulin levels never return to zero. The rise in insulin levels is dependent upon the type of food - as previously mentioned carbohydrates that have a high glycaemic index produce a much more marked rise in the insulin levels and this then takes longer to return to zero.

If insulin levels are never allowed to return to zero it means that the cells of the body are constantly saturated within insulin and their automatic response to this is to say “no more” and this results in insulin resistance. Because the body is trying to keep blood glucose within strict parameters the net effect of insulin resistance is for the pancreas to produce even more insulin and this then creates a vicious cycle in that more insulin increases insulin resistance. This is a significant factor in the development of obesity.

The treatment of type 1 diabetes is to replace the deficient insulin with medication in the form of insulin injections (insulin is a peptide and therefore cannot be taken by mouth as it would be broken down just like any other protein in the gut before it is absorbed).

The treatment of type 2 diabetes is somewhat more complicated. There are a number of different medications that can be used to either promote insulin secretion by the pancreas or to reduce insulin resistance (or increase insulin sensitivity). However, at some point these treatments may fail to be effective – and in these particular patients once again insulin is required to keep blood sugars under control. Unfortunately, this perversely has a compounding effect on insulin resistance because as previously mentioned insulin resistance is accelerated by too much insulin.

An important part of reducing insulin resistance is dietary manipulation in the form of restricting the amount of carbohydrate in the diet. But more importantly reducing the frequency of which food, in particular carbohydrate, is taken in. And this is exactly the rational for using intermittent fasting in the treatment of obesity and importantly the reason why it works.

For further information about see the presentation entitled Intermittent Fasting.