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What’s the difference between GI, GL and ‘low glycemic’? Which should I use and does it really matter?
We are often asked this question. Hermin Halim who recently graduated MNutriDiet from the University of Sydney sorts out the confusion.

Hermin Halim

Many people’s lives have been better off with the low GI diet as the success stories published in GI News show month after month where we see people achieving weight loss, better blood sugar control, better overall health, better stamina, and so on. What makes GI stand out is that no real counting is needed (such as calorie counting) – by choosing a low GI food rather than a higher GI food, you see a lower and steadier rise in blood glucose while eating the same amount of food. Looks straightforward, but still, quite a few people find it confusing.

So what is GI all about? Principally, GI is based on the quality (the characteristics) of carbohydrate in food; that is, how quickly or slowly the blood glucose will rise with the consumption of this food. It is worked out from the increase in blood glucose after eating 50 g carbohydrate portion of the food, compared with 50 g pure glucose – the form of sugar that is present in our blood.

Yet some people are still quite resistant to GI – they say that they find it confusing and complicated, and point to ‘healthy’ foods with a high GI like watermelon. Well yes, watermelon does have a high GI, but this shouldn’t discourage anyone from eating it, because a typical serving size (a 120 g/4 oz wedge) only contains 6 g available carbohydrate so will have very little impact on your blood glucose levels. In fact, to get 50 g carbohydrate from watermelon, you would need to eat 1 kg watermelon – and that’s a lot!.


And this is where what’s called GL (glycemic load) come into the picture because it takes into account both the GI (carbohydrate quality) and the amount of carbohydrate in the portion size. Sounds more practical than GI, doesn’t it? But it’s not that easy. This is because there are two routes to a low GL – a food can either have a low GI or be low in carbs (like watermelon). So although watermelon has a high GI, its GL or glycemic impact is low because it has so little carbohydrate. So it won’t spike those blood glucose levels.

So why bother about GI if eventually you have to calculate both the total carbohydrate content and the GL? This is where one of the strongest objections to GI (and the best support for GL) came from. The proponents of GL even back it up with some ‘compelling’ evidence on the benefits of low GL diet in weight loss, heart disease, diabetes, obesity, and certain cancers. And interestingly, the food doesn’t have to be low GI. Low carbohydrate, high protein diet was also effective in all these, even diabetes, so why should we have more carbohydrate? After all, people tend to prefer meat, chicken, cheese, and egg more than the tasteless grains and cereals. This adds fuel to the already heated controversy. So how do GI experts react to this?

Prof Jennie Brand-Miller makes the point that while there are lots of ways to lower the GL, ‘at present it is not clear that all will be equally beneficial.’ It is true that one could lower the GL by lowering the carbohydrate content, but is it achievable? Professor Brand-Miller points out two main flaws of low-carb diet. Firstly, that it may not be healthy because of its high saturated fat content – and this fat increases the risk of heart disease, so probably would cancel out the reported benefits of low carbohydrate diet anyway. Secondly it is not feasible as this involves limiting even moderate sources of carbohydrate (such as fruit and dairy products) which contain lots of important nutrients.

A low GI diet, on the other hand, is healthy and is in line with the Guide for Healthy Eating in Australia (and the Healthy Eating Pyramid elsewhere) which suggests that our everyday eating should be based on grains – high carbohydrate, low fat, nutritious foods – and with them, fruit, vegetables, low-fat dairy, and protein foods that are low in saturated fats (including nuts and legumes). With the low GI diet, you’ll be eating the five food groups in the balanced amount without missing out on nutrients. You’ll also find it easier to follow, as it’s close to your usual eating pattern. For a diet to be easy to be effective in the first place, it has to be easy to stick to. That’s why Professor Brand-Miller concludes, ‘the GI appears to be more effective’.