There are currently more than two million Canadians with diabetes, and by the end of the decade, this number is expected to rise to three million. With a battery of health professionals around the world vigorously pursuing research in diabetes control and elimination, Professor Thomas Wolever of the department of nutritional sciences is one of U of T’s foremost diabetes researchers.
Though the focus of Wolever’s recent research surrounds the glycemic index (GI), a measure of the quality of carbohydrates in starchy food, his career began with a fascination with fibre. The “fibre hypothesis,” a theory that attributes the cause of most diseases to a lack of fibre in the diet, was at the crux of Wolever’s research in the early seventies.
“[The fibre hypothesis] really grabbed me because as a medical student, it seemed to me that for most of the diseases which people suffered from, like cancer, heart disease, and diabetes…there were no good treatments,” said Wolever. “If I really wanted to make an impact as a doctor, then this was the area to become involved in.”
By the mid-seventies, the medical community had generated many theories about how fibre worked, but little data. Wolever, then a master’s student, focused his research on how fibre affects glucose absorption in the intestine. His early paper turned out to be one of the most highly cited papers in the fibre field and paved the way for today’s definitions of soluble and insoluble fibre.
“It was very exciting and romantic. I was on the cutting edge of research doing simple studies with antiquated equipment and finding amazing results-it actually worked!” said Wolever.
Despite his studies in medical school, a passion for research led Wolever to the development of the GI, a measure of the quality of starchy carbohydrate in foods like in bread, rice, and potatoes. The GI has broad implications in health and disease, from influencing our mood and memory to physical performance. Since Wolever’s definition of the GI, scientists have shown that the GI of dietary carbohydrates influences risks for diabetes, heart disease, some types of cancer, and may be useful in the management of some of these conditions.
The problem lies in measuring the GI of food and the lack of low-GI options for food staples, like bread.
“We need to get more evidence on the health implications of GI, but at the same time, we need more low-GI foods to help obtain that evidence,” said Wolever.
Wolever’s current research in GI falls under two main categories. One branch of research addresses the problems in measuring GI, the factors that influence the variation of GI in certain starchy foods, and how to produce low-GI foods. The other branch focuses on proving that GI is important in preventing diseases like diabetes.
But there are very few clinical trials showing that a dietary intervention based on low-GI foods actually prevents the development of diabetes. Of today’s prevention methods, weight loss and exercise have been proven to slow the progression of “pre-diabetes”-a condition where blood glucose levels are higher than normal but not high enough to be diagnosed as diabetes-to diabetes by about 60 per cent.
Weight loss and exercise, according to Wolever, isn’t the solution, but regulating the GI of food may prevent diabetes or heart disease altogether. The only problem is proving it, which would involve mounting a massive clinical trial involving thousands of subjects. Wolever has recently completed a small trial investigating a low-GI food diet in over a hundred diabetic participants looking at blood sugar levels and cardiovascular disease risk factors.
In another small-scale study, Wolever looked at the effects of a low-GI diet on reducing intramyocellular fat, the type of fat lost during weight loss and the probable cause of insulin resistance. If these studies are successful, Wolever may soon have the support to conduct a larger study.
“The role of GI in established diabetes may move more from being a way to improve [blood sugar levels], although it will always help fine-tune that, to being a way to prevent the complications of diabetes.”
