Carbohydrate is an essential part of our diets, but not all carbohydrate foods are equal. The Glycemic Index (GI) is a relative ranking of carbohydrate in foods according to how they affect blood glucose levels. Carbohydrates with a low GI value (55 or less) are more slowly digested, absorbed and metabolised and cause a lower and slower rise in blood glucose and, therefore usually, insulin levels.
There are three classifications for GI:
Individual food portion:
Low: 55 or less
Mid: 56 – 69
There is a real need to define the difference between a low GI diet and/or meal and a low GI food. Because a low GI food is defined as 55 or less, everyone has made the reasonable assumption that a whole diet that averages 55 or less is a low GI diet. In fact the average Australian and American diets already have a GI of around 55–60 because we eat fruits and dairy foods which are naturally low GI. So, to reduce the risk of chronic disease, we believe we need to aim lower and suggest that 45 is a better cut-off point for a low GI diet.
Thus for the whole day the classifications are:
Low: 45 or less
Well, we 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 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 heart disease and diabetes, 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.