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Low GI diet advised for diabetes

Nuts and beans could be a better bet than bran-flakes for people with type 2 diabetes

People with type 2 diabetes could be better off eating more beans, lentils and nuts rather than high-fibre cereals such as bran-flakes and whole wheat, according to the latest research published in the Journal of the American Medical Association.

Canadian researchers found that people who stuck to a diet of so-called 'low-glycaemic index' foods such as nuts and pulses saw a greater improvement in their blood glucose and cholesterol levels than those on a diet high in fibre-rich cereals.

The Glycaemic Index ranks foods according to how much they raise a person's blood glucose levels. As foods are digested they are broken down into sugars that enter the bloodstream and give us energy. Foods that are high on the index are broken down into sugars very quickly, causing a 'spike' in blood glucose levels. Low GI foods, however, have less impact, releasing their sugars more slowly and providing a more sustained source of energy.

Following a low GI diet has been found to help stabilise blood sugar levels but, according to the study, there is a lack of research into its effectiveness for diabetes control. There is also limited evidence so far that the diet can lower the risk of cardiovascular problems such as heart disease.

In the study, David J A Jenkins and colleagues from the University of Toronto compared the impact of a low-glycaemic index diet against a high-cereal fibre diet on blood glucose and cholesterol levels in 210 patients with type 2 diabetes. The patients were all taking medication to lower their blood glucose levels. Each was randomly assigned one of the two diets to follow for a total of six months.

Those on the low GI diet were asked to eat more of the following low GI foods: beans, peas, lentils, nuts, pasta, rice boiled briefly and low GI breads, such as pumpernickel, rye and quinoa and flaxseed. For breakfast, they could eat low GI cereals such as oat and oat bran.

In the high-cereal fibre diet, patients were advised to take the 'brown' option when choosing carbohydrates, eating more traditional high fibre foods such as whole grain breads, whole grain breakfast cereals, brown rice and potatoes with skins. Three servings of fruit and five servings of vegetables were encouraged on both treatments.

Researchers measured the levels of a substance called haemoglobin A1c in the blood that is used to determine long-term blood glucose levels as well as levels of HDL and LDL cholesterol in all patients at the start and end of the study period. They found that blood glucose levels decreased by an average 0.50 per cent in the low-GI diet group compared with 0.18 per cent in those on the high-cereal fibre diet.

The low GI dieters also saw a greater improvement in the ratio of HDL or 'good' cholesterol vs LDL or 'bad' cholesterol levels in their blood. Whereas levels of HDL cholesterol decreased a little in the high-cereal group, there was a modest increase in the low GI diet group.

"Lowering the glycaemic index of the diet improved glycaemic control and the risk factors for coronary heart disease (CHD)," say the authors of the study. "These data have important implications for the treatment of diabetes. Low-glycaemic index diets may be useful as part of the strategy to improve glycaemic control in patients with type 2 diabetes taking antihyperglycemic (blood sugar reducing) medications."

"The Glycaemic Index is certainly useful as it can guide people towards foods which release their energy slowly and don't cause sudden increases in blood sugar levels," says Natasha Marsland, dietician and care advisor for the charity Diabetes UK. "However, there is a fair bit of overlap between the two diets tested in this study. Some of the whole grain foods in the low GI diet will also be in a high fibre diet too.

"We recommend people eat a varied diet and wouldn't advise that those with diabetes stop eating high-fibre cereals simply because they have a higher GI ranking. Many low GI foods such as apples, porridge oats and pulses are high in soluble fibre whereas the high-fibre cereals such as bran flakes or wholemeal bread contain more insoluble fibre. Both are important to good digestive health.

"Eighty per cent of people with type 2 diabetes are overweight at the time of diagnosis so our dietary advice is often about a low sugar, low fat diet with an emphasis on portion control. Low GI foods such as porridge or pasta might be good for blood sugar levels but not if you eat a huge bowlful! Moderation is the key and that means you can enjoy small amounts of high GI foods, too."

The Glycaemic Index

Foods containing carbohydrates are assigned a number from 1 to 100 based on how much they raise blood sugar levels, with 100 being the score for pure glucose. Foods are usually grouped into high (greater than 70), low (less than 55) or moderate (56-69).

Low GI foods

• Pasta
• Rye bread
• Nuts
• Lentils
• Beans

High GI foods

• Corn flakes
• Rice crispies
• White bread
• Mashed potatoes
• Scones
• Dates

For a more detailed list of low GI foods, visit: www.the-gi-diet.org

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Information on this site is for interest only and is not a substitute for professional medical advice. You should consult your own doctor about any specific health concerns.

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