Lifestyle Choices

Over the last fifty years, the incidence of Type z diabetes (in which too much insulin is produced) has rocketed, in parallel with the incidence of obesity. This is despite us eating less — often a lot less — than our parents and grandparents. Some scientists believe that the availability of refined foods, particularly the increase in the amount of fat from diet from about 25 per cent to the present 35 per cent, plus the lack of physical activity, causes changes in muscle which are responsible for the development of Type z diabetes and obesity.

In diabetics, levels of glucose are higher than they should be in the blood, either because it is not taken up rapidly enough into tissues such as muscle, heart and fat, or because too much glucose is produced by the liver.

Glucose is a primary fuel for many tissues, and for the brain and nervous system, which powers through about 120 grams of glucose a day, it is almost essential. In extremis, it will make do with a substitute derived from fat, known as ketone bodies, but if it is doing this, then you are likely to be pretty much in extremis yourself — either starving, or dying from insulin-dependent diabetes.

The proper name for diabetes is diabetes mellitus, which means literally ’sweet fountain’, referring to the fact that a high concentration of glucose in the blood spills over into the urine and gives it a characteristic malty smell. It is said that doctors from ancient times detected diabetes by a taste test — whether this is apocryphal or not is unknown.

Diabetes is in fact two separate diseases with the same end result: raised blood glucose (hyperglycaemia). The first, insulin-dependent diabetes, is an autoimmune disease, which starts early in life, often in childhood, in which the patches of tissue in the pancreas that produce insulin are destroyed. Normally insulin is made in response to the appearance in blood of glucose, which has been absorbed from the gut following a meal. Carbohydrates like potatoes and bread release most glucose when digested.

By far the greater number of people suffering from diabetes have the sort known as Type z or late-onset diabetes. This, as its name suggests, appears in later life, after forty usually, although it can occur at a younger age than this in some communities, for example in Indians living in Britain. Here there is not a lack of insulin — far from it, for insulin levels are higher than normal — but rather an inability of the normally insulin-sensitive tissues like muscle and the liver to respond to it.

So how does insulin work, in a normal, healthy person? After a meal, rising levels of glucose cause insulin to be secreted. Insulin drives glucose into muscle tissue (which makes up about a third of the total body weight in a lean person), including that of the heart (which is a big lump of muscle) where it will be stored as glycogen, the precursor fuel needed to power muscle exertion. Insulin also prompts a switch from the liver generating glucose — a process which ensures that between meals the blood concentrations of glucose can be kept more or less constant — to packing glucose away into storage depots. Glucose is stored either as glycogen, a carbohydrate fuel, or as triglycerides, fats similar to those found in olive oil, corn oil or lard. Significantly, for our obesity tale, insulin also drives glucose into body fat, where it is stored as triglycerides.

If insulin is not present at all — as in insulin-dependent diabetes, then muscle tissue cannot build up the reserves of glycogen fuel that it needs during exertion. The effect of no insulin is to put the body in a state which is very similar to starvation. In desperation, it responds by breaking down the triglycerides stored in fat which then, as fatty acids, can be used as an alternative fuel by muscle and heart — but not by the brain which, as we have seen, needs glucose.

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