G.I. values show a certain degree of variability, both from day to day and between people. In non-diabetic subjects, the average day-to-day variation is 22 per cent (ie the G.L value varies by an average of 22 per cent). In people with type 2 diabetes, it is 16 per cent, but in individuals with type 1 diabetes, it is as high as 30 per cent. This means we should not expect to see precisely the same blood sugar levels after one particular food from one day to the next.

As is the case with any biological response there is quite wide variation between subjects ie the G.I. in one person may be double that in another. However, it is dear that subjects tend to ‘track’ well, giving high or low or intermediate responses on a consistent basis. In practice, therefore, foods will show the same ranking in terms of G.I. factor in different subjects.

Why are there different G.I. values for the same food in different publications?

In some instances, there is a difference between two results but it is small and not statistically or biologically important. For example, G.I. factors of 70 and 80 for white bread are not considered very different. The difference is within the error of the methodology. A difference of 20 units, say 60 and 80, is considered important in a clinical sense and is usually statistically significant as well.

There may also be differences due to variations in the food itself. Rice is a good example of this. Genetically determined differences in the amylose content of rice means that different varieties of rice have very different G.I. factors. Basmati rice has a low G.I. factor and Calrose rice has a high G.I. factor. In the early days of G.I. research, the variety of rice was not specified.

Again, the same food processed in different ways can produce very different G.I. factors. Breads containing a lot of intact whole grains will have a lower G.I. factor than normal soft white sandwich bread. Packaged breakfast cereals, on the other hand, are processed in similar ways all over the world and their G.I. factors are very similar in Canada, Australia and elsewhere.

A third reason for the differences is the use of two reference foods, bread or glucose. However, it is easy to convert from one scale to the other using the factor 1.4 (equals 100/70). For example, if the G.I. factor of a food is 80 when bread is the reference food, its G.I. factor on a scale where glucose equals 100, is 80 divided by 1.4 (equals 57).

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Don’t let your diabetes routine spoil things for you. What are the options?

1.     Miss out on your evening dose that night. If it is a small dose and you are careful with what you eat and pretty accurate this might be all right. Check your blood glucose when you get home, and if it is high give a small dose of quick acting insulin before supper.

2.     Refuse the invitation and go home for insulin. Not a good idea. Even if you didn’t want to stay you shouldn’t use diabetes as an excuse.

3.     Ring up your parents and ask them to drive over with your insulin and syringe. This would answer your problem but would it be fair to ask? Only you (and they) could answer this.

4.     Stay for the meal and plan to have a modified dose of insulin when you get home. About two thirds of the usual dose at supper time would probably cover you satisfactorily, but check your blood glucose. You could need a little more of the quick acting insulin if it is high. I favour the fourth option but discuss it with your parents when the occasion arises.

I am going on a school camp. What should I do about blood tests and insulin?

The best way to enjoy your camp is to make sure you don’t have a hypo, or let your diabetes get out of control. Be prepared for activity, perhaps delayed meals and unusually late nights.

Take a good supply of syringes, an extra bottle of each insulin (in case of accidents) blood testing strips, urine-ketone strips and a good supply of carbohydrate exchanges, such as dried food, barley-sugar, other lollies and biscuits. It may be best to take the blood testing strips that don’t need a meter (BM Test Glycemie 20-800 or Glucostix).

Make sure a responsible adult knows about your diabetes and what to do if you have a hypo.

Make sure that your friends know that you will need insulin injections and may need extra food or sugar.

Divide your supplies of insulin and syringes into two packs. You carry one and a responsible friend or adult carries the other. A lost pack could otherwise spoil the camp.

Discuss what to do about blood tests and insulin in advance with your doctor. Here is my suggestion: Do a blood test when you get up. If it is low have some sugar at once while waiting for breakfast. If it is high and you don’t feel well check for urine-ketones. You could need extra quick acting insulin if ketones are positive but check in advance with your doctor how much you would give.

Otherwise have a slightly reduced dose of insulin because you will probably be pretty active at camp and need less insulin because it works more efficiently this way. Have extra carbohydrate during the day if you are very active, especially hikes or swimming.

If a meal is delayed have one or two exchanges at the usual time while you wait for the meal. Have your evening dose of insulin just before the evening meal, but reduce the dose to prevent a night time hypo.

Do a blood test before you go to bed. If it is low have an extra starch exchange to make sure that you don’t become hypoglycemic during the night.

With these precautions you should have no trouble – and your parents won’t need to worry about you either.

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