All people with diabetes are advised to eat a healthy, balanced diet. This is a way of eating that is recommended for everyone.

However, people with Type 1 diabetes need to do more than just eat 'healthily'. The quantity, type and timing of your food choices are just as important as making sure that you have had your daily quota of fruit and vegetables.

Here, we focus on the effects of food on blood glucose levels and the relationships between insulin, diet and blood glucose levels in the management of Type 1 diabetes.

Carbohydrates, blood glucose and insulin

Carbohydrate foods have the greatest effect on blood glucose levels and it is the starchy foods - bread, cereals, potatoes, pasta, rice etc. - that you will need to pay most attention to you.

Carbohydrate foods are mostly broken down into glucose by digestive enzymes. The glucose is then absorbed from the intestine into the bloodstream (usually 1 - 2 hours after eating) and this causes the blood glucose level to rise. Insulin is needed so that the body's cells can take this glucose from the bloodstream and either use it for energy or store it for later. People who do not have diabetes will produce just the right amount of insulin to cope with the rise in blood glucose that occurs after a meal. Insulin on demand allows the person without diabetes to keep blood glucose levels within the normal range, even after a meal rich in carbohydrates.

Getting the balance right

If you have Type 1 diabetes then your body no longer produces insulin; you have to inject it yourself. In order to keep the blood glucose level close to normal after eating, you need to inject just the right amount of insulin to deal with the food that you eat. It is also important that the injection is timed right, so that the insulin is arriving in the bloodstream at the same time that the glucose from the digested food is being absorbed from the gut.

If there is too little insulin (for the amount of glucose coming from the digested food) then the blood glucose level will rise too high (hyperglycaemia). If there is too much insulin (or not enough glucose coming from the digested food) then the blood glucose level will fall too low (hypoglycaemia).

So, your food intake needs to be closely matched by your insulin injections. This is why you will need to consider not only what you eat, but how much you eat, and when.

Different food types

The overall effect of a meal on the blood glucose level will depend on the different types of foods making up the meal.

Glycaemic Index

Different types of carbohydrate foods are digested at different rates and therefore have different effects in terms of raising the blood glucose level after a meal. Some foods are quite rapidly digested to glucose (e.g. cornflakes), whilst others take longer for the glucose to hit the bloodstream (e.g. All-Bran^TM). The effect of different carbohydrate foods on blood glucose levels has been quantified by the Glycaemic Index (GI). Foods with a low GI cause less of a spike in post-meal blood glucose than those with a high GI.

Sugar

It is still widely believed amongst the general population that people with diabetes should avoid eating sugar because it causes a rapid increase in blood glucose levels. This is not true! Table sugar, which we sprinkle on our cornflakes, actually causes less of a spike in blood glucose than the cornflakes themselves. Sucrose*, surprisingly, has a lower GI than cornflakes.

As part of healthy eating, we are all advised to cut down on sugar - this is because it has little nutritional value, it does little to satisfy the appetite and it's a source of 'empty calories'.

*Important note:

Table sugar is not the same as glucose. Table sugar is called sucrose and is a disaccharide - it contains two sugar molecules: one fructose and one glucose. Table sugar needs to be broken down by digestive enzymes before the fructose and glucose can be absorbed. Glucose is absorbed quickly because it does not need to be broken down (digested) first.

Protein and Fat

Carbohydrate foods have the greatest effects on blood glucose levels because they are mostly digested to glucose, which is absorbed from the intestine straight into the bloodstream. However, proteins and fats in the diet affect blood glucose levels too.

Excess protein in the diet that is not needed by the body is converted to glucose by the liver. This means that consuming large amounts of protein can result in an increase in blood glucose levels several hours after eating.

The most significant effect of fat is probably to slow down the rise in blood glucose after a meal. Fat delays the rate at which the stomach empties - this has the knock-on effect of slowing down the absorption of glucose from digested carbohydrate foods. You might think that this is a good thing, but remember that a high-fat diet is not necessarily a healthy diet.

Putting the theory into practise

Remember, your aim is to keep blood glucose levels close to normal. Eating causes the blood glucose level to rise; the aim of your insulin injections is to minimise 'post-meal spikes' in blood glucose without causing hypoglycaemia (low blood glucose).

In order to understand the relationship between the food that you eat, your blood glucose levels and the insulin that you inject you will need to learn about the different types of insulin that make up your insulin regimen. You should know when the insulins act and which parts of your insulin regimen aim to cover which meals.

Should my meals be tailored to my prescribed insulin regimen?

In years gone by, people with Type 1 diabetes were advised to stick to quite a rigid meal schedule, which was determined by their insulin injections. Some insulin regimens still call for this to a certain extent. However, these days it is generally recognised that it is better to derive an insulin regimen that suits the individual person's lifestyle.

So, in most cases insulin should be tailored to your food intake and not the other way round. This assumes that you are eating a healthy and nutritious diet that fulfils your needs.

To start with then, you will need to find the right insulin doses for an 'average' day in your life. In practical terms, you will need to eat a normal healthy diet, trying to eat roughly the same at the same time each day. Using blood glucose monitoring to guide you, the timing and/or dose of your insulin injections can be adjusted. Your healthcare team will help direct you in this. Your aim is to establish a routine, which gives reasonable control of your blood glucose levels, and fits in with your lifestyle. Then you can work from this baseline, fine-tuning your control and perhaps also introducing more flexibility.

Snacks

An important role of diet in managing Type 1 diabetes is preventing low blood glucose levels (hypoglycaemia).

Some insulin regimens require you to have snacks in between meals in order to prevent hypoglycaemia. Snacks are not always necessary though, so check with your doctor and/or dietitian to see if you need to snack between meals.

A bedtime snack is, however, essential for all people with Type 1 diabetes. This ensures that blood glucose levels don't fall too low during the night.

Snacks are also very important before exercising, especially if the activity does not form part of your regular daily routine. This is to prevent exercise-induced hypoglycaemia.

Accommodating change

In practise, most people have a regular insulin regimen, which is tailored to their 'average' day. The insulin dose and timing of the injections relates to how much is usually eaten and when. In theory, you will know that your insulin dose is just right for your 'normal' eating pattern. Any changes you might make to your usual day may need to be catered for by an appropriate tweaking of the insulin dose. Your diabetes team will be able to give you personal advice on how to make adjustments to cope with changes to your normal schedule.

As a general rule, more food (especially carbohydrates) needs more insulin, otherwise the blood glucose level will rise too high. Less food (especially carbohydrates) needs less insulin, otherwise the blood glucose level will fall too low. It is important to get the adjustment just right - or you may find that you have overcompensated for the change and given too much or too little insulin.

Use blood glucose monitoring to find out whether your adjustments are working; make a note in your diary of the changes you made and learn from experience. The most informative times to test are before eating and then 1 - 2 hours after your meal.

Delayed or missed meals are probably the most common cause of hypoglycaemia. Take steps to avoid low blood glucose levels if you know that you are not going to be able to eat your usual meal. Have an extra snack to keep you going and keep an eye on your blood glucose level.

Fine tuning your diet

Use your blood glucose test results and your knowledge of the effects of food on YOUR blood glucose levels to fine tune your diet for better control.

Here is a summary of some of the main points for your consideration: