Low GI diet helps type 2 diabetics, study says

TORONTO - Type 2 diabetics who eat a diet rich in slower-to-digest foods like nuts, beans and lentils have better blood-sugar control and a lower risk of cardiovascular disease, compared with those whose diets rely more heavily on cereal-fibre foods, researchers suggest.

In a study of 210 people with Type 2 diabetes, University of Toronto researchers had half of the participants eat a low glycemic-index diet that emphasized beans, peas, lentils, nuts, pasta, parboiled rice, slow-to-digest breads like pumpernickel and cereals such as large-flake oatmeal.

The remaining subjects were advised to consume a healthy "brown" diet recommended by the American Diabetes Association, which includes whole grain breads, whole grain breakfast cereals, brown rice, potatoes with skins, and whole wheat bread and crackers.

All participants, who continued taking their medications for reducing elevated blood glucose (sugar), also were encouraged to eat three servings of fruit and five servings of vegetables daily.

After six months, the group on the low glycemic diet was found to have better blood glucose control than the brown diet group, as determined by levels of a specific substance in red blood cells.

As well, those on the lower glycemic diet had improved overall cholesterol levels, with more good cholesterol, said lead author Dr. David Jenkins, a clinical nutritionist at St. Michael's Hospital in Toronto.

"I think the changes are significant because, remember, these are diabetic folk who are already on one, two or three glucose-lowering medications," Jenkins said Tuesday. "So many of them are topping the balance at the maximum number of medications that you'd naturally want to give a diabetic."

Some participants also lost weight as a result of being on the low glycemic diet, and some were able to cut back on their glucose-control medications, he added.

The study, published in Wednesday's edition of the Journal of the American Medical Association, suggests that by improving their cholesterol levels with the low glycemic diet, diabetics cut their risk of cardiovascular disease, which can lead to a heart attack or stroke.

But that's just one of the many complications that can arise from uncontrolled diabetes - and that a low glycemic diet would perhaps help prevent, Jenkins said, explaining that slower-to-digest foods avoid the rapid surge and fall of glucose that occurs with quickly metabolized products.

Such fluctuations in blood sugar are believed to give rise to free radicals, which can harm blood vessels and other tissues throughout the body.

"So I think what this does," said Jenkins, "is this now gives another tool ... for getting the blood glucose levels down, which is tremendously important to stop diabetics from going blind, losing their kidneys and succumbing to other problems."

Co-author Dr. Cyril Kendall, an associate researcher at St. Michael's Hospital, said the low glycemic diet would be used as an adjunct to other strategies to lower blood glucose.

"What this study indicates is that the quality of carbohydrates is important," he said. "So not only should we be looking at total carbohydrate in a diet, but the quality of the carbohydrate. And we should be aiming at low glycemic-index foods."

It may come as a surprise to some, but "pasta's an extremely good food" when it comes to keeping stable blood glucose levels, noted Kendall. "It's got a bad reputation over the last few years."

But pasta - even white-flour pasta - is actually broken down by the digestive system much more slowly than either white or whole wheat bread, he said, so its glucose is not absorbed into the bloodstream all in one go.

"So pasta's a very important low glycemic carbohydrate source."

Pasta fagioli, a rich Italian soup made with beans and pasta, would be an ideal example of a diabetic-friendly dish, added Jenkins.

Historically, North Americans and those from other developed countries typically ate low-glycemic foods. That all changed with the advent of highly processed food like white bread made from refined flour, the authors say.

"Many of the foods that we've deserted, such as beans and lentils and chickpeas and pumpernickel bread ... these sorts of food actually are good for us," he said. "And we tend to pass them by.

"And we tend to crave those foods that are white and fluffy and melt in the mouth. And, unfortunately, because they melt in the mouth, they also melt in the intestines very rapidly and give big surges in blood glucose after a meal."

"And that's one of the things we have to get under control," said Jenkins, who believes that adopting a low-glycemic diet could also help prevent Type 2 diabetes from developing in those at high risk for the disease.

More than two million Canadians have diabetes, with about 90 per cent of them afflicted with Type 2, according to the Canadian Diabetes Association. Also known as adult-onset, Type 2 diabetes is a disease in which the pancreas either doesn't produce enough insulin or the body cannot properly use the insulin it does make.

The researchers have applied for a grant to perform a larger and lengthier study that would investigate the long-term effects of eating a low glycemic diet on diabetics' cardiovascular systems.