Prof Jennie Brand-Miller
Can the GI be applied to everyday meals?
Criticism of the GI has focused on unpredictable outcomes of blood glucose values after meals because of variations in fat, protein and fibre content. Most of our meals consist of a variety of foods – not just a single food. Even though GI values are derived from testing single foods in isolation, we and other scientists have found that it is possible to predict the ranking of blood glucose responses among meals that consist of several foods with different GI values.
Concerned about the methodology of recent studies showing unpredictable responses, we and our co-researchers at the University of Toronto’s Department of Nutritional Sciences conducted studies with mixed meals on two groups of healthy subjects in Toronto and Sydney. We had previously done smaller studies, but we wanted to revisit the question, using more meals and variety in two different centres with judiciously selected foods. This time, 14 different test meals were used in Sydney and Toronto, and the food combinations reflected a range of typical breakfast choices.
Despite the variations in food factors, relative blood glucose responses remained consistent with GI measures. In fact, we were startled by the degree of predictability. The carbohydrate, fat and protein composition of the meals varied over a wide spectrum. The glucose responses varied over a fivefold range, and yet 90 per cent of that variation was explained by the amount of carbohydrate in the meal and the GI values of the foods as given in published GI tables. We found that the GI works just as predictably whether subjects consume a single portion of one item or a normal meal; we reported these findings in the American Journal of Clinical Nutrition.
More recently, we systematically tested 121 single foods in 1000 kJ portions and 13 mixed meals in 2000 kJ servings. There were wide variations in carbohydrate, fat, protein and fibre content. We found that the GI and/or glycemic load were best predictors of the magnitude of hyperglycaemia and insulinemia, outstripping carbohydrate content in every instance. Indeed, among the mixed meals, carbohydrate was not even a significant predictor. These findings were also published in the American Journal of Clinical Nutrition.
Another study in a recent issue of the American Journal of Clinical Nutrition concluded that there is substantial uncertainty in predicting the GI of mixed meals. The limitation with this study, however, is that the investigators chose to study just 3 mixed meals with a very narrow range in predicted GI (51, 53 and 63). Not surprisingly, they found that they couldn’t distinguish between the two lower GI meals. The potato meal produced the highest response as we might expect. Ideally, in studies such as this, it makes sense to study more meals across a wider spectrum of predicted GI.
New GI Values from SUGiRS
Arnott’s Vita-Weat Lunch Slices
These crispy slices make a great base for your favourite toppings for lunch or a snack. You’ll find them in supermarkets in Australia. Here are the GI values for the two flavours we tested:
- Soy Linseed and Sesame: GI 52 – 1 slice provides 19g available carbohydrate. The GL of this size serving is 11
- Sunflower Pumpkin and Canola – GI 59 – 1 slice provides 19g available carbohydrate. The GL of this size serving is 13.
If you want to compare these crispy slices with similar products – or a slice of bread or piece of toast – here’s the nutrition information product data per 100 grams from the packaging (it wasn’t on their website when we checked just before posting this issue online):
- Soy, Linseed & Sesame per 100 grams – Energy: 1720kJ; Protein: 14.5g; Fat: 11g (includes 1.3g saturated fat); Available carbohydrate: 57.1g; Fibre: 11.7g; Sodium 465mg
- Sunflower, Pumpkin and Canola per 100 grams – Energy: 1720kJ; Protein: 14.3g; Fat: 11g (includes 1.4g saturated fat); Available carbohydrate: 58.1g; Fibre: 10.9g; Sodium 473mg
Sanitarium Up&Go Breakfast Yoghurt
Available in a 200g ‘squeezie pack,’ it’s a convenient way to grab a healthy yoghurt for breakfast when you are on the go. You’ll find this product in the chilled section in your supermarket and convenience outlets (Victoria Australia only). The nutrition and ingredient information is on the Sanitarium website HERE.
- Strawberry and Vanilla flavours: GI: 44 (both) 1 serve (200g) provides 35g available carbohydrate. The GL of this size serving is 15
New GI Values from GI Labs
Hollywood Foods More Than Pasta
More Than Pasta is fresh pasta produced artisan style with an original Italian pasta machine to give you that ‘homemade’ pasta experience. Co-owner Gabriella Micallef says that: ‘it’s a unique product as it has been specifically developed to be significantly higher in protein (15g per 60g serving) and fibre than traditional pastas.’ Available fresh or frozen, you can buy it in Toronto and selected outlets in Canada. Visit www.hollywood-foods.com for availability and nutritional analysis. More Than Pasta:
- Fettuccine: GI 31 – a 60g (2oz/1/3 cup) serving provides 17g available carbohydrate, 5g fibre and 15g protein. The GL of this sized serving is 5.
- Linguine: GI 31 – a 60g (2oz/1/3 cup) serving provides 17g available carbohydrate, 5g fibre and 15g protein. The GL of this sized serving is 5.
GI testing by an accredited laboratory North America
Dr Alexandra Jenkins
Glycemic Index Laboratories
20 Victoria Street, Suite 300
Toronto, Ontario M5C 298 Canada
Phone +1 416 861 0506
Research Manager, Sydney University Glycemic Index Research Service (SUGiRS)
Human Nutrition Unit, School of Molecular and Microbial Biosciences
NSW 2006 Australia
Phone + 61 2 9351 6018
Fax: + 61 2 9351 6022
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