It has long been suspected that a high sugar diet over a long term period may lead to an increased risk of developing diabetes. But there has been little or no evidence to support this idea, with studies on the role of any aspect of the diet in the development of diabetes difficult to conduct.

Researchers from the Royal Victoria Hospital and Queen’s University Belfast have just published the results of a clinical trial looking at the effects of high sugar intake on insulin resistance (said to be a precursor of Type 2 diabetes) and vascular health in 13 healthy nondiabetic men. Sharing their findings in this month’s Diabetes journal, Dr Steven Hunter and his team of researchers report that those who received 25% of their calorie intake from sucrose (sugar) as part of a balanced, weight maintaining diet for 6 weeks showed no difference in their degree of insulin resistance, compared to a eucaloric (calorie matched) diet providing 10% of energy as sucrose (control).

In this study, the 25% treatment diet provided on average 200g sucrose per day compared with 80g sucrose from the control (10%) diet (around the average for a British adult).

Dr Hunter of the Royal Victoria Hospital said: ‘Sugar has traditionally been linked to the development of diabetes. These findings challenge that thinking, and show that intakes of more than double that currently recommended do not appear to have an adverse effect on markers of diabetes risk.”

The study saw 13 healthy men receive either a high-sugar diet (providing 25% of their energy) or a diet providing 10% of their energy as sugar for a period of 6 weeks. After the 6 weeks, subjects ‘crossed over’ to receive the other treatment for a further 6 weeks. Treatments were separated by a four week wash out period, during which the subjects returned to their usual diet.

The diets for each period were closely matched in overall macronutrient (carbohydrate, fat and protein) composition. The only difference was in substituting sucrose (sugar) for starch. Insulin resistance was measured by the research ‘gold standard’; a two-step glucose clamp.

Furthermore, the high sucrose diet showed no significant adverse effects on a number of other metabolic and physiologic parameters, such as elasticity of the arteries (known as vascular compliance) which impacts on risk of heart disease, and glycaemic profiles.

This study showed that an intake of sucrose two and a half times above average consumption levels showed no adverse effects on this important marker of diabetes risk. This study does not therefore support the notion that sugar intake, within a broad range that covers the intake of the majority of British adults has any adverse effect on the risk of diabetes.

Diet can have a large impact on risk of type 2 diabetes; the strongest evidence for a link exists with saturated fat. Dr Hunter advises that the best way of reducing the likelihood of developing diabetes is through lifestyle changes. He adds “It is likely that other dietary factors such as excess calories and lifestyle factors such as physical inactivity and weight gain may be more important than carbohydrate type.”

In people at risk of type 2 diabetes, a diet rich in carbohydrate and low in fat appears to offer protection against insulin resistance. In addition, being of a healthy body weight and maintaining an active lifestyle will help reduce the risk of developing type 2 diabetes.

Insulin resistance is a common but often silent disorder which occurs when the body does not respond appropriately to the effects of insulin (see below). Insulin resistance can lead to, and is a feature of, the more serious condition, type 2 diabetes (non-insulin dependent diabetes). It is also an independent risk factor for atherosclerotic vascular disease. Any affect of a high sucrose diet on insulin resistance is therefore a reliable indicator of its likely influence on the risk of diabetes and atherosclerosis.

Insulin, a hormone produced by the pancreas, is needed for normal glucose, fat and protein metabolism. Insulin controls the amount of glucose in the blood by enabling glucose to enter cells (e.g. muscle and liver cells) which need glucose for fuel. With insulin resistance the body’s cells do not respond fully to the effects of insulin and/or the body cannot produce enough insulin to overcome this defect. This ultimately leads to raised blood glucose. Having blood glucose that is too high (hyperglycaemia) is dangerous to health, for example, long-term hyperglycaemia is associated with an increased risk of kidney and eye problems.

Fat metabolism is also affected by insulin resistance raising the risk of heart disease, the most common cause of death amongst people with diabetes.

On a global scale, insulin resistance and type 2 diabetes are becoming increasingly common. Whilst genetics account for some degree of susceptibility to these disorders, lifestyle factors such as diet and physical activity levels can have a large impact on risk. Insulin resistance is closely involved in type 2 diabetes, and is thought to be a precursor to the disease.