U of T researchers find glycemic index effective in composite meals
Study shows GI reliable predictor of blood glucoseResearchers in the University of Toronto's Department of Nutritional Sciences have some reassurance for diabetics and carb-counters. The glycemic index (GI), the table that lists the quality of carbohydrates in more than 750 common foods, works just as predictably whether subjects consume a single portion of one item, or a normal meal.
The GI was developed 25 years ago at U of T by Professors Thomas Wolever and David Jenkins. The table has become an important tool for the management of non-insulin diabetes and a reference point for popular carbohydrate-reducing diets. Carbohydrates are converted to glucose in the bloodstream and blood glucose levels are key indicators. Recent criticism of the GI has focused on unpredictable outcomes of blood glucose values in meals because of variations in fat, protein and fibre levels.
"The good news it that the GI index works" says Wolever. "For sensible people it makes a lot of sense. It's simple proportional measure – like mixing paint."
Concerned about the methodology of recent studies done elsewhere showing unpredictable responses, Wolver and his associate, Professor Jennie Brand-Miller of the University of Sydney, Australia, each conducted studies on two groups of healthy subjects. Fourteen different test meals were used in Sydney and Toronto, and the food combinations reflected typical breakfast choices such as juice, bagels and cream cheese, etc. Despite the variations in food, blood glucose responses remained consistent with GI measures.
"We had previously done much smaller studies. We revisited the question, using more meals and variety in two different centres with judiciously selected foods. I was startled by the degree of predictability," says Wolever. "The carbohydrate, fat and protein composition of the meals varied over a wide spectrum. The glucose responses varied over a five-fold range range, and 90 per cent of the variation was explained by the amount of carbohydrate in the meal and the GI values of the foods as given in published GI tables. The concept works." The results are published in the June issue of the American Journal of Clinical Nutrition.
The Canadian Diabetes Association affirms the value of the GI. "We definitely feel it's an invaluable tool in helping manage blood glucose and recommend it for diabetes education," says Sharon Zeiler, senior manager, nutrition initiatives and strategies. The basic principles of the GI are also applicable to a range of conditions, ranging from mood and memory to cardiovascular health and weight management.
Mary Alice Thring
University of Toronto
Glycemic Index Laboratories
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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