Food for Thought

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It’s time to raise the bar and lower the GI cut-offs for fast foods and convenience meals

The GI was introduced back in 1981 to rate the glycemic character of the carbohydrate in individual foods like bread, breakfast cereal, rice, pasta, apples etc. The purpose was to exchange one carbohydrate source with another for snacks and in your meals (e.g. replacing a high GI breakfast cereal like corn flakes with a low one like natural muesli). The decision behind the cut-offs for high GI (70 or higher) and low GI (55 or lower) foods at that time was based on the scatter of GI values among single foods that had been GI tested.

We are often asked about mixed meals including fast foods and convenience meals and the effect of extra protein and fat in the food on GI and blood glucose response. Eaten alone, protein and fat have little effect on blood glucose levels, but that’s not to say they don’t affect your blood glucose response when they are combined with a carb-rich food. Protein will stimulate additional insulin secretion, resulting in lower blood glucose levels. Protein and fat both tend to delay stomach emptying, thereby slowing the rate at which carbohydrate can be digested and absorbed. So a high fat meal will have a lower glycemic effect than a low fat meal even if they both contain the same amount and type of carbohydrate.

Because SUGiRS (Sydney University Glycemic Index Research Service) is being asked to test an increasing number of fast foods and convenience meals, we think is that it’s high time to review the cut-offs for mixed meals. When it comes to defining a low GI meal such as a pizza (crust + toppings) or hamburger (bun + pattie + mayo + ketchup + salad + pickle), we should be looking at a figure of around 45 or less so that the GI value reflects the effect of the fat and protein in the meal.

We suggest the 45 or lower would be the appropriate new cut-off for a low GI fast food or convenience meal. Why 45? Well, we now know from numerous observational cohort studies around the world that the daily average GI of the diet of people in the lowest quintile (20% of the population) is about 40–50. Similarly, in a meta-analysis published in Diabetes Care of 15 experimental studies investigating the role of low GI diets in managing diabetes, the daily average GI was 45. Since this average GI has been proven to have significant health benefits in people with existing diabetes and in reducing the risk of chronic diseases like diabetes and heart disease, and importantly, people can and do achieve it in real life, we believe a GI of 45 or less is what we all need to be aiming for in mixed meals like burgers or pizzas or toasted sandwiches or filled subway-style rolls and in our overall diet.

Here are the new cut-offs we are suggesting for fast foods and convenience meals:

  • Low GI 45 and under
  • Medium GI 46–59
  • High GI 60 and over

Based on some of the fast foods we have already tested, here’s how it looks:

Table of GI cut-offs for mixed meals