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Researchers criticize Health Canada evaluation of glycemic index

Toronto, December 11, 2013

By Leslie Shepherd

Dr. Livia Augustin
Dr. Livia Augustin

Researchers at St. Michael’s Hospital, where the glycemic index was developed, have criticized a Health Canada evaluation of the scale that measures how fast and how high individual foods raise blood glucose levels.

Health Canada published a paper in June saying it could be “misleading” to add GI values to food labels and that it “would not add value” for consumers trying to make healthier food choices.

“Unfortunately, Health Canada does not seem to understand the glycemic index, or else it would have come to different conclusions,” said Dr. Livia Augustin, of the hospital’s Clinical Nutrition and Risk Modification Centre. She wrote a letter to the editor of the British Journal of Nutrition, along with other members of the International Carbohydrate Quality Consortium, a committee of leading nutrition experts, rebutting the Health Canada paper. It was published today.

The director of the Risk Modification Centre, and a co-author of the letter, is Dr. David Jenkins, who developed the concept of the glycemic index in the early 1980s as a way of explaining how different carbohydrates affect blood glucose and to find out which foods were best for people with diabetes.

High GI foods—such as white bread, most breakfast cereals, potatoes and rice — produce a spike in blood glucose and insulin, which means people are hungry again soon after eating. This can lead to overeating and obesity, and higher risks of Type 2 diabetes or cardiovascular disease in the long-term. The carbohydrates in low GI foods—including pasta, beans, lentils, berries, apples and certain whole grains such as barley and oats –are broken down more slowly, so that people get more gentle raises in blood glucose and insulin and they feel full longer.

“I am pleased that Health Canada is recognizing the glycemic response, or the blood sugar after eating a carbohydrate, as an important health target,” Dr. Jenkins said. “But I am surprised that it would not accept the glycemic index, which we devised to standardize the glycemic response and make the concept useful for people to use and compare foods which they would not be able to do with the non-standardized glycemic response of foods.”

The GI is used in many diets, including the South Beach Diet, and is included in the Canadian dietary guidelines for people with Type 2 diabetes.

The International Carbohydrate Quality Consortium recommended at a conference in Italy last summer that the GI be included in national dietary guidelines and food labels as a way to help reduce the risk of heart disease and Type 2 diabetes and possibly to assist with weight loss.

The Health Canada paper, published in The American Journal of Clinical Nutrition, said the GI measure has poor accuracy and precision for labeling purposes and does not vary in response to the amount of food consumed. It said that putting GI values on food labels could have the unintended consequence of becoming the predominant criteria for food selection, even when some low-GI foods are not consistent with the Canada Food Guide.

Dr. Augustin, who has a PhD in nutrition, said the methodology used to calculate the GI of foods is recognized by both the World Health Organization and the International Standards Organization.

“Concerning accuracy and precision of nutrition labels, one cannot let perfect be the enemy of good,” said Dr. Augustin and the ICQC group. “For example, both whole grains and fibre claims are permitted on food labels, despite the fact that the definition and measurement of each varies among countries and is neither perfect nor precise. A whole grain product may contain only 50 per cent whole grains, according to the U.S. Food and Drug Administration and there is marked disagreement on what fibre is and how it should be measured.”

Responding to Health Canada’s assertion that the GI does not vary in response to the amount of food consumed, Dr. Augustin said that it is not supposed to, as the GI reflects carbohydrate quality rather than quantity. That’s where the glycemic load, or GL, comes in. It tracks both the GI of a food and the amount consumed. The carbohydrate in watermelon, for example, has a high GI. But there aren’t many carbs in watermelon (which is mostly water), so the fruit’s glycemic load is relatively low.

Dr. Augustin said she agreed with Health Canada that when making healthy food choices, the GI should not be used in isolation from such things as saturated fat, fibre and whole grain content but should complement other dietary advice. She said foods that carry the GI symbol in Australia must also meet strict criteria for calories, saturated fat and sodium, and, where appropriate, fibre and calcium. Those nutritional criteria are consistent with international dietary guidelines and were developed in consultation with experts from the University of Sydney and diabetes organizations. Surveys in Australia indicate one in four consumers look for healthy low GI foods when shopping.

“I think it is remarkable that if the GI were not a reliable tool and were of no value, that a large body of scientific literature in fact shows many health benefits of low GI foods in people with and without diabetes and that low GI diets are associated with reduced risk of coronary heart disease, Type 2 diabetes and certain cancers in many large studies internationally.” Dr. Augustin said. “Taken together, Health Canada’s evaluation misinterprets and misrepresents current scientific evidence in part by taking GI out of the context of a healthy diet.”

About St. Michael’s Hospital

St. Michael’s Hospital provides compassionate care to all who enter its doors. The hospital also provides outstanding medical education to future health care professionals in 27 academic disciplines. Critical care and trauma, heart disease, neurosurgery, diabetes, cancer care, care of the homeless and global health are among the Hospital’s recognized areas of expertise. Through the Keenan Research Centre and the Li Ka Shing International Healthcare Education Centre, which make up the Li Ka Shing Knowledge Institute, research and education at St. Michael’s Hospital are recognized and make an impact around the world. Founded in 1892, the hospital is fully affiliated with the University of Toronto.

Media contacts

For more information, or to arrange an interview, contact:

Leslie Shepherd
Manager, Media Strategy
416-864-6094
shepherdl@smh.ca