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Carbohydrates: what, when and how much in diabetes?

Carbohydrates (CHO) are essential to our diet and those with diabetes, however people without diabetes produce ample insulin to break down the sugars produced from carbohydrate intake. Why then do carbohydrates play such an important part in the life of those with diabetes?

Over the years opinions have varied, although back in 1797, John Rollo,1 an army physician, became the first to recommend a low carbohydrate, high protein diet for treating diabetes. In the 1980s, the Dose Adjustment For Normal Eating (DAFNE) course was introduced, and part of its' teaching was on the subject of carbohydrates, including counting them and increasing your insulin dose to control the resulting blood sugars. DAFNE was all about trying to help those with type 1 diabetes live as normal a life as possible, so there soon followed the advice that these people could eat as much as they liked as long as they counteracted this with a sufficient dose of insulin.

It appears that there is now increasing evidence to support low carbohydrate regimes to manage 'diabesity,' the co-existence of diabetes and obesity. Last year a meta-analysis2 examined the effects of low CHO diets on cardiovascular risk factors. The low CHO diets led to substantial improvements in many risk factors, including weight decrease and cholesterol. 

Most nurses involved in diabetes care know it is important for those with diabetes to control what they eat, and those with type 1 diabetes in particular need to control their carbohydrate intake. In order to have well-controlled blood sugars in diabetes, three things need balancing. These are insulin, food (particularly carbohydrates) and physical activity. These are the fundamentals of managing both main types of diabetes, and when they are not appropriately balanced, there will be wide variations in blood sugar levels. 

In type 1 diabetes, where the pancreas fails to produce its' own insulin supply, insulin must be injected. However following diagnosis of type 2 diabetes, a reduction in food intake, primarily carbohydrates, may sufficiently reduce the blood sugar levels, alongside regular physical activity. In practice this is extremely difficult to achieve. Physical activity that is moderately vigorous improves insulin sensitivity in the body so that body tissues can break down the sugars more readily. 

Those with type 2 diabetes have an insufficient insulin supply and are likely to have a degree of insulin resistance, meaning that the tissues of the body cannot utilise the limited amount of circulating insulin. Many appear unaware that carbohydrates or starchy foods are converted into sugars in the body. Often people say, “I have cut out sugar from my diet” or “but I don't eat anything sweet”, as if that is the only way their blood sugars rise. Therefore it is important that we explain simply where the blood sugars come from and keep reminding them regularly that eating carbohydrates will raise their blood sugars. 

Those with type 1 diabetes will need an external source of insulin as soon as they are diagnosed (or very soon after) in order to keep themselves alive. This is most commonly via subcutaneous injection. Most people with type 1 diabetes are then taught at some stage about counting their carbohydrate intake, in order to be able to calculate the correct doses of Insulin. The DAFNE course provides structured education for those with type 1 diabetes, and as mentioned earlier, is often where patients learn how to balance their food (CHO) intake and insulin doses.

 Over time this seems to have been interpreted as being able to eat as much as you like when you have type 1 diabetes, as long as you compensate with an appropriate dose of insulin. However there is evidence to suggests that this may not be either the best or the only way.3 One study is summarised below.

A 46-year-old man who had type 1 diabetes for 15 years went on a DAFNE course at St Thomas Hospital to try and improve his diabetes management. On this course he was told he could eat what he wanted, as long as he counted his CHO intake and matched it with the appropriate dose of insulin. He was also encouraged to eat pasta and white rice and 60g CHO per meal. While on the course his sugars stayed fairly level, but afterwards he found he still had major hypoglycaemic episodes, his overall control was no better and his eyes were deteriorating.

On moving to New York, his doctor there was appalled by his large doses of insulin and his overconsumption of carbohydrates. His American doctor advised him to reduce his CHO intake as much as possible and fill up with greens and salads. The man reluctantly did this and over a period of time three things happened:

1. His doses of insulin dropped dramatically.

2. His blood sugars were vastly improved.

3. He lost 33lbs in weight.

What had happened? Eating food freely, particularly CHOs raises blood sugars and therefore larger doses of insulin are required to counteract this. Insulin is a hormone, which is sometimes (illegally) used by sports people as it helps to build muscle (and also weight). Therefore, if insulin doses are continually increased to normalise blood sugars elevated by carbohydrate intake, then there may also be weight gain, often seen in those with type 2 diabetes.

In both type 1 and type 2 diabetes, the body is struggling to regulate the sugars produced from carbohydrates due to the shortage or absence of insulin in the body. Is it logical to advise these patients to eat carbohydrates freely and inject insulin in appropriate doses to control the elevated blood sugars? What might be more beneficial is to advise patients, that on the occasions when they may have overeaten carbohydrate and other foods, they should compensate with an increased dose of insulin.

If CHO intake is controlled or reduced even, then the dose of insulin will not need to keep increasing, and in fact it may reduce. One currently popular method of managing carbohydrates (in those without diabetes) is by eating low glycaemic index (GI) foods. The glycaemic index is a means of ranking carbohydrate foods based on rate of conversion to blood sugars. High GI foods are those carbohydrates, which are rapidly converted to glucose in the blood, while low GI foods are those which take longer to be converted to sugars. Low GI foods would appear a better option for those with diabetes, as they will then have more control over their blood sugar levels.

Calculating the exact GI of foods can be hard when they are cooked or eaten with other foods. It is easier to focus on eating more unrefined, high fibre or whole grain foods, which are processed more slowly in the body (complex CHOs) and limit refined, sugary foods (simple CHOs, see Table 1). However even then there is still a place for fruit and vegetables in the diet. The main thing is to take into account the portion size and the total amount of carbohydrate being consumed; GI may help, but does not replace the necessity to count carbohydrates.

Recently The Times4 highlighted the fact that children in the UK today are generally eating too much carbohydrate, which may be contributing to the current obesity epidemic. As a population, we all need nutritional education - not only those with diabetes - so that our intake of carbohydrates, especially refined ones, is in keeping with our physical activity. People with diabetes who may be dependant on insulin injections, or oral medications are just much more vulnerable.

Those with type 1 diabetes are constantly having to try to balance carbohydrate intake and insulin dosage, and this presents a significant challenge to them, and not surprisingly, mistakes may at times happen in these calculations. These are complex calculations, which are described by Sussman et al5 as an “intensive challenge” and include all the following aspects: CHO intake, ratio of CHO to insulin, blood glucose levels, glucose correction factor and the target for correction. Such calculations are seen to be one of the most major problems for intensive insulin users.5

Help is now available, due to the manufacture of a new class of blood glucose meter. The INSULINX meter is a new meter, designed to assist those who trying to balance their food/carbohydrate intake with their insulin doses. It contains an inbuilt automated bolus calculator, and also has the ability to store the following data: insulin and medication information, food intake, amount of exercise taken and health information. The 'advanced' mode calculates what insulin dose is required based on food/CHO consumption, and current dose of insulin. It also calculates their correction factor, so they can learn how to adjust their doses more accurately.

This meter has only been available relatively recently and is becoming increasingly popular. There have been reports of overall insulin dose reduction and often an accompanying weight loss. For patients who don't count carbohydrates, there is an 'easy' mode, to help them, based on normal food intake. Diabetes patients need ongoing support in trying to manage their diabetes. With such a tool now available to help them in this constant juggling, it is essential that we equip them with such tools, and train them, so their diabetes management can truly improve.



Carbohydrates form a significant element of diabetes management in both type 1 and type 2 diabetes and we cannot ignore this fact. Our routine management of those with diabetes must include regular education on balancing food (especially CHOs) with insulin - wherever it comes from - and physical activity. It should not be a surprise to any patient with diabetes that when their carbohydrate intake increases, so will their blood sugars, and if this continues over time, there will be resultant weight gain. It is our responsibility to provide those with diabetes the tools necessary to manage their diabetes. 

Both education and technology have a part to play and there are many tools available to guide them in their eating habits. Often our initial advice will need re-iterating: food intake (carbohydrate control), insulin (from their pancreas or injected) and physical activity are the basics in managing their diabetes, whatever drugs we may prescribe them to help.



1. Rollo J. An account of two cases of the diabetes mellitus with remarks as they arose during the progress of the cure. London: Dilly; 1797.

2. Santos FL, Esteves SS, da Costa Perreira A et al. Sytematic review and meta analysis of clinical trials of the effects of low carbohydrate diets on cardiovascular risk factors. Obesity review 2012:13:1048-1066.

3. Hirst J. Is a High Carb diet poison to Diabetics? Insulin Dependent Diabetes Trust. September 2012; 6-7.

4. Little M. Five foods you must cut back on. The Times Weekend. 23 March 2013; 7.

5. Sussman A, Taylor E J, Patel M, et al Performance of a Glucose Meter with a built in Automated Bolus Calculator versus Manual bolus calculation in insulin using subjects. Journal of Diabetes Science and technology 2012; 6:339-344