Reliable facts in short supply for advice on what diabetics should eat

Almost every day, some new piece of dietary advice is issued to the public – usually implausible enough to grab the attention. Diabetes sufferers will have been told that grapefruit could protect against the illness; that dairy foods lower the risk of diabetes; and that zero-calorie sweeteners increase it.

Yet, as with similar claims about food and cancer, the relationship between illness and diet is hard to pin down. One reason is the lack of robust long-term experiments, as well as the complexity of diets and chronic illnesses.

However, nutritionists and scientists agree on one thing when it comes to food and diabetes: overeating leads to weight gain and overweight people are more likely to develop type 2 diabetes than lean people.

In addition, some people have a genetic disposition that leads them to develop diabetes without necessarily being overweight.

Dr Gojka Roglic, technical officer of the World Health Organisation’s diabetes programme, says: “Obesity is the strongest risk factor for type 2 diabetes. Not all obese people develop type 2, only those that have an innate genetic susceptibility – but even they are less likely to get it if they are not overweight.”

Obesity rates worldwide have climbed far more rapidly than expected – by 67 per cent over the past decade to 500m people, which in turn has led to rates of diabetes escalating far beyond the Geneva-based WHO’s forecasts.

Why does being overweight trigger the risk of getting diabetes?

Broadly-speaking, excess weight is stored as fat under the skin. But once these safe fat stores are exhausted, the fat spills over into organs such as the liver and round the pancreas, interfering with the pancreas’s production of insulin and the liver’s function in regulating sugar levels. This results in higher blood sugar levels, which can lead to type 2 diabetes.

As long as people do not overeat, whether what they eat makes a difference in terms of the risk of developing type 2 diabetes, is a matter for debate.

Recent controversy has swirled around high fructose corn syrup (HFCS) – a byproduct of corn used to sweeten processed foods and drinks.

One study published two years ago by Oxford university and the University of Southern California, suggested that HFCS consumption could increase the risk of diabetes. Basing its evidence on countries such as the US, which has the highest consumption of HFCS, the research found the prevalence of diabetes in such nations was 20 per cent higher. “This study doesn’t prove that HFCS causes diabetes,” warned Diabetes UK, a charity that funds research. “For example, it does not show that individuals with diabetes consumed higher levels of HFCS or that this consumption was the key factor leading to their condition.”

At the same time, the International Journal of Obesity published a study – part-funded by the Corn Refiners Association – suggesting there was no evidence to pin the US obesity epidemic on HFCS.

Stephanie Dunbar, director of nutrition at the American Diabetes Association, says: “Our position is that people with, and at risk of diabetes, should limit or avoid intake of sugar-sweetened beverages (from any caloric sweetener including high-fructose corn syrup and sucrose) to reduce the risk for weight gain and worsening of cardiometabolic risk profile.”

Clearly, further research is needed, which is why Diabetes UK commissioned more work to assess the link between fructose and type 2.

The research, carried out by Loranne Agius, professor of metabolic biochemistry at Newcastle University, shows that dietary fructose is a much more powerful agent than glucose in causing fatty liver and changes in liver function, including the insulin resistance that increases the risk of developing type 2 diabetes.

Since the starch in carbohydrate breaks down into glucose in the body, she concludes there is no evidence from long-term clinical studies to support the assumption that low-fat, high-carbohydrate diets are healthier than ones low in carbohydrate and high in fat. This view has contributed to a rise in consumption of pasta, rice, and potatoes.

In the meantime, experts see great scope for preventive measures: from labelling foods to taxation.

The World Health Organisation cites studies showing that in China, increases in the price of unhealthy foods reduced intake, while in the US, cheaper healthy foods led to a 68 per cent rise in consumption.

The WHO adds that exercise plays an important role: moderate exercise of 150 minutes a week cuts the risk of diabetes by 27 per cent.