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Is it time to stop promoting carbohydrates to people with diabetes?

The Diabetes Professional Conference earlier this month included a debate on whether it is time to stop promoting carbohydrates to people with diabetes.

Because we get so many questions and carbohydrates from people with diabetes, we asked the two debaters to summarise their argument.

“For” by Dr Trudi Deakin, a research dietitian who is Chief Executive ofX-PERT Health:

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Dr Trudi Deakin

"There are three main nutrients in the diet: carbohydrate, protein and fat. Carbohydrate (both starch and sugar) is building blocks of glucose and when digested, glucose is released into the blood.

Thus, carbohydrate is the only nutrient that directly impacts on blood glucose levels.

The history

In the early 1900s, doctors advocated that severe dietary restriction, called “starvation therapy”, was the only hope for the management of diabetes. That remained the single approach to prevention of the diabetic coma until the first use of insulin in humans in 1922.

Once insulin therapy became the mainstream treatment, people were to restrict carbohydrate and get their energy from protein and fat instead.

Carbohydrate liberation

Scientists believed that the high fat and protein diet was contributing to the long-term complications of diabetes (heart disease, stroke, kidney disease, blindness and amputations) and therefore in the 1990s the restriction on carbohydrate was lifted.

People with diabetes were encouraged to “base their meals on starchy carbohydrate” and consume at least half of their daily calories from carbohydrates. This remained the case even after a large UK clinical trial demonstrated that diabetes complications were largely caused by poor blood glucose and blood pressure control.

Dietitians were taught to advise people that, if they fancied something sweet, they should eat it after starchy carbohydrates as this would stabilise their blood glucose level. But there was no evidence for this statement and all it did was increase the amount of carbohydrate people were consuming, which in turn deteriorated blood glucose control.

This meant that, for many people, promoting starchy carbohydrates resulted in a vicious circle of poor diabetes control, increased prescribed diabetes medication and weight gain. This is why, in 2003, the Diabetes UK nutritional guidelines for diabetes acknowledged that consuming over 50% of calories from carbohydrate wasn’t suitable for everyone and in 2011, the recommendations were further revised to state that there isn’t an ideal proportion of carbohydrate for optimal blood glucose control.

Carbohydrate requirement

Glucose is essential for survival. The brain requires 130 grams of glucose per day and the carbohydrate reference intake (RI) for a healthy adult is 260 grams per day, double the minimum requirement to ensures sufficient carbohydrate is available to meet physical activity demands. But three things should be noted:

  • the 260g per day is not a target but a reference;
  • it is a reference for a healthy adult who is moderately active and normal weight;
  • if the relevant amount of carbohydrate is not consumed, the body can make it from protein and fat supplies.

Individual needs

The reference range of 260 grams of carbohydrate per day does not suit every person with diabetes. In Type 1 diabetes, people may not wish to take the high doses of insulin required to match that level of carbohydrate and, in Type 2 diabetes, insulin may not work properly at clearing the glucose from the blood (insulin resistance) and additional carbohydrate can aggravate the problem, especially if the person is overweight and not physically active.

People with diabetes require structured carbohydrate awareness education so that they understand which foods contain carbohydrate and develop the skills to assess their own diet and be able to work out the amount and type of carbohydrate they are eating.

They can then set themselves goals to ensure they are consuming the right amount of carbohydrate to match their physical activity levels, also taking into consideration their weight and level of diabetes control.

In the UK, many of the starchy staple foods release the glucose quickly into the blood i.e. they are high GI foods. But when people are advised to base their meals on carbohydrate, many of them end up eating over 300 grams a day.

Through our experience of delivering structured education, many people reduce their carbohydrate intake to between 130-260 grams per day and are able to improve their diabetes control and body weight as a result. To date, lower carbohydrate diets have not shown any negative effects.

If people wish to experiment with lowering their daily carbohydrate intake to below the 130 grams per day, they should be told that the long-term outcome is not yet known and, if they would like to persevere, they should be supported in doing so by their diabetes care team.

So, in summary, we should stop promoting carbohydrates to people with diabetes because:

  • The blanket approach of recommending over 50% of calories from carbohydrate is not beneficial for many people with diabetes;
  • There is no evidence for the ideal percentage of calories from carbohydrate and some evidence for the beneficial effect of lower carbohydrate diets;
  • Carbohydrate requirements differ based on individual preference, body weight, diabetes control, insulin resistance and physical activity levels;
  • People need carbohydrate awareness education so that they can assess their carbohydrate intake and set goals to meet their individual needs."

“Against” by Carla Gianfrancesco, Specialist Diabetes Dietitian at Sheffield Teaching Hospitals NHSF Trust:

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Carla Gianfrancesco

"Healthy carbohydrate foods such as wholegrains, pulses, fruit, vegetables, milk and yoghurt should be encouraged in the diets of people with diabetes because they have been shown to contribute to a healthy heart and circulatory system and so reduce risk of health problems common in diabetes such as heart attacks and stroke.

By restricting carbohydrate, the diet becomes unbalanced and over time this could result in vitamin and mineral deficiencies; higher blood fat levels due to higher fat intake; and kidney and bone problems from having too much protein.

When the body digests carbohydrate, they are turned into glucose, the body’s main source of fuel for energy. If the body does not get enough of it, it is forced to make fuel from fat and protein instead. A side effect of this is the production of a compound called ketones.

But most cells in the body prefer glucose as their fuel and this is particularly the case with the nervous system, which includes the brain. This means that they struggle to function without it and so it is important you get at least 130g of carbohydrate a day to meet the brain’s need for glucose.

"Don't know long-term health effects"

This is also the threshold for preventing the production of ketones, which is important because we do not know the long-term health effects of the body producing ketones when on a low carbohydrate diet.

Another problem with low carbohydrate diets is that they lead to low levels of glycogen, which is a sort of glucose that is stored in the muscles and liver. Glycogen is important for giving us energy between meals and provides energy to keep active. And glycogen is particularly important for people with diabetes because the body also relies on glycogen when blood glucose levels fall below normal levels and so not having enough of it increases risk of hypos and makes them more difficult to recover from.

With so many possible negative effects on health, it would be a mistake to move towards restricting carbohydrates without clear evidence that there are benefits of this approach.  And because it is important to make sure people with diabetes actually enjoy their diet, food choices should only be limited when there is strong scientific evidence that limiting them will bring health benefits.

So what is the evidence? Major research studies have shown that conventional low fat, high fibre diets similar to those promoted by Diabetes UK do both prevent Type 2 diabetes and help people who already have it to manage it.

Studies of different diets have not given any conclusive evidence that there is extra benefit in following a low carbohydrate diet over other approaches such as low fat diets. Where studies have found benefit, it has been difficult to tease out exactly what is causing the benefit. For example, was any positive benefit coming from the fact that the study participants were having less carbohydrates or was it was it due to the higher amount of monounsaturated fat consumed or that they ate less calories?

In most of these studies, people lost weight but we think this is likely to be down to having fewer calories rather than the type of diet they followed. This is why, based on the evidence currently available, Diabetes UK recommends weight control as the main way to control blood glucose levels in people with Type 2 Diabetes rather than following a specific diet.

Anecdotal reports suggest that some people with Type 1 diabetes choose to follow a lower carbohydrate diet for various reasons, including not wanting to have to carbohydrate count or to make their blood glucose level more predictable.

Interestingly, in a small study in Sweden that promoted a low carbohydrate diet for people with Type 1 diabetes, after four years only one in four people continued to follow it and the authors suggest this approach may be an option for just  a small proportion of people with Type 1 Diabetes.

Studies in Type 1 "inconclusive"

Studies evaluating the effects of different carbohydrate intakes on Type 1 diabetes have been inconclusive but an analysis of the diets of more than 500 people in the Diabetes Control and Complications Trial showed that a higher fat and lower carbohydrate intake was linked to worse blood glucose control in these people. Generally, it is thought that self management skills which enable people to accurately match their carbohydrate intake and insulin is the most important thing for Type 1 diabetes control when it comes to what you eat.

Low carbohydrate diets have also been shown to be a good option for losing weight, though in the longer term are no different from more conventional diets at keeping the weight off.

They are therefore one of many options people can choose from when considering the best approach for them. Tailoring the advice to a person’s circumstance and involving the person with diabetes in the decisions is an essential aspect of diabetes care and that would be under threat if we went for a blanket guidance for carbohydrates to be restricted.

As Type 2 Diabetes progresses, giving people carbohydrate awareness education to enable them to be able to monitor their carbohydrate intake is important for achieving good blood glucose control. The education includes being able to identify  healthy carbohydrate sources, an understanding of diabetes treatments and the best way to spread carbohydrates out through the day to match treatment and importantly, ways of  estimating how much carbohydrate is in which foods.

To improve blood glucose levels, people are encouraged to reflect on their carbohydrate intake and, where relevant, results of home blood glucose monitoring and make changes to the timing, distribution or amounts of carbohydrate according to need.

So in summary, to stop promoting carbohydrates in the diet of people with diabetes would go against current research findings and has many potential negative effects on health. It is important that food choices are not restricted unnecessarily to allow individuals to choose a dietary strategy that suits their lifestyle and that they feel confident that they can follow over many years.

Carbohydrate awareness education should be provided for all people with diabetes as this effective way of enjoying a variety of carbohydrate foods in the diet whilst still maintaining control of blood glucose levels."

Tracy Kelly, Head of Care for Diabetes UK:

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Tracy Kelly

"The carbohydrate debate remains topical and can be quite confusing for both people with diabetes and the general public when all people want to know is what they should be eating and what will keep them healthy - or healthier.

We should be careful that we don’t get stuck on the words “promote”, “encourage”, “avoid” and miss the key messages from the debate.

Both Trudi and Carla agree that everyone needs some carbohydrate and that an individualised approach should be adopted in relation to how much carbohydrate a person should eat based on the goals that they are trying to achieve. People with diabetes need to understand what foods contain carbohydrate, how to estimate carbohydrate portions and how to monitor their effect on blood glucose levels - and education is pivotal to achieving this balance.

We agree that carbohydrates are needed and that for good health, people should aim to get most of their carbs from vegetables, fruit, whole grains and dairy products rather than from other sources, especially those that contain added fats, sugars and salt.

It is important to remember that the amount of carbohydrate eaten is a strong predictor of glycaemic response, so monitoring the total carbohydrate intake is key to achieving good glycaemic control.

The quantities however should depend on your individual goals and you should be supported by your diabetes team when making this decision. We are firm believers that diabetes self-management support is essential for all people with diabetes and its necessary to improve any outcomes as people with diabetes are largely responsible for managing their diabetes."

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