Low GI or Low GL, what’s the difference?

Whether you’re trying to lose weight, control diabetes or prevent disease, it’s important to be aware of the effects of the sugar in carbohydrates on your body and in particular, your blood sugar level.

Carbohydrates provide fuel for your body to burn for energy.  However, the modern diet is often heavily laden with carbohydrates which release their sugar content very quickly and have a detrimental effect on your health.

In an ideal world, we want to see the level of sugar circulating in the bloodstream to be fairly stable throughout the day, supplying our energy needs. If we were to plot this on a chart, we’d want it to look something like this:


The highs and lows correspond to the amount of sugar in the bloodstream, depending on whether you’ve just eaten or are getting hungry.

When you eat a carbohydrate with a fast releasing, high sugar content, the level of sugar in the blood stream rises sharply.


When there is too much sugar in the bloodstream, your pancreas releases insulin, taking the surplus sugar out of the blood and dumping it in fat stores.   The more sugar there is in the blood, the more insulin is released and this can cause the blood sugar level to fall too low and you get hungry.


This is when many people will reach for a sugary snack or drink to give them a boost of energy.  This works for a brief period, until more insulin is released and their energy dips again.  And yes, you’ve guessed it, they eat another high carb snack or meal.  So they can end up with the blood sugar level yo yo-ing throughout the day.

 Ultimately, this can lead to a situation where your body becomes “insulin resistant” that is, it ignores the insulin instruction to dump excess sugar into fat stores and levels can become dangerously high.  This leads to Type 2 diabetes, which is becoming more and more common.

So how do you avoid this and control the level of sugar in your bloodstream?

Back in 1981, the Glycaemic Index  (GI) was invented by Dr Thomas Wolever and Dr David Jenkins at the University of Toronto.  The GI is a ranking of carbohydrates on a scale from 0 to 100 according to the extent to which they raise blood sugar levels after eating. Foods with a high GI are those which are rapidly digested and absorbed and result in marked fluctuations in blood sugar levels. So the GI tells us about the quality of a carbohydrate.

Sugar has a GI value of 100 and other foods are measured against that.  People were advised to eat mainly foods with a low GI (55 or less), or moderate GI value (56 -69).  It was suggested that high GI value foods (70+) should be combined with  a low GI value food, or avoided altogether.

Here’s some examples of GI values:

Food GI value
Burgen mixed grain bread 34
Muffin 54
Special K 54
Cola 63
Croissant 67
Weetabix 69
Wholemeal bread 69
Crumpet 69
Bagel 69
Swede 72
Watermelon 72
Gluten free bread 79
Cornflakes 84
Puffed Wheat 89
Rice Milk 92


So you can see that Muffins, Special K were considered fine to eat.  Cola, croissants, bagels were fine in moderation whereas watermelon was in the “to be avoided” group.

The big problem with only looking at how fast the sugar content of a food hits the bloodstream, is that it takes no account of just how much sugar there is in the food. Because some foods typically have a low carbohydrate content, Harvard researchers created the GL rating system that takes into account the amount of carbohydrates in a given serving of a food.

The GL looks at both the quality of the sugar – how fast it releases, and the quantity.  The GL means the total “Glycaemic Load” on the body.  It’s worked out by using a simple formula.  Take the GI value of a food, multiply it by the amount of carbohydrate in a food and divide by 100.

So, why is this important? First, let me explain that if you want to keep blood sugar levels stable,  maintain your ideal weight and enjoy good health, you need to aim for each of your 3 main meals having a GL value of 15.  If you want to lose weight, then you’d aim for each of the 3 main meals having a GL value of 10.  In order to keep blood sugar levels stable through the day, you’d add in 2 snacks mid morning and afternoon, each with a GL value of 5.

When we add the GL value into the table above we can begin to see the significance of the GL rating system:


Food GI value GL value
Burgen mixed grain bread 34 2 slices = 4 GL
Muffin 54 11 GL
Special K 54 30g serving 14 GL
Cola 63 250ml = 14 GL
Croissant 67 1 = 17 GL
Weetabix 69 2 biscuits = 11 GL
Wholemeal bread 69 1 thick slice = 9 GL
Crumpet 69 1 = 13 GL
Bagel 69 1 = 24 GL
Swede 72 150g = 7 GL
Watermelon 72 120g = 4 GL
Gluten free bread 79 1 slice = 10 GL
Cornflakes 84 30g serving = 21 GL
Puffed Wheat 89 30g serving = 16 GL
Rice Milk 92 250ml = 14GL


Under the GI rating system, Special K would be considered fine to eat, having a score of 54.  But we can see that because it is all unrefined carbs it has a GL value of 14!  Okay if you’re wanting to maintain your weight, but not if you want to lose weight.

A bagel, just squeezes into the “eat in moderation” bracket yet has a massive GL value of 24!  That blows 2 main meals and 1 snack in just 1 bagel!!!

Puffed wheat has a high GI score of 89 which is reflected in the GL value of 16.  One meal and 1 snacks worth!

However, look more closely at watermelon with a GI value of 72 which puts it into the “avoidance” group.  It has so little sugar (just 6 grams) in it that the GL value is only 4, making it fine to eat.  If we do the math with watermelon we can see how this works out:

72 x 6 = 432  divided by 100 = 4.32   rounded to 4GL per serving.

When you start looking at the GL value of foods, it becomes evident how easy it is to blow your blood sugar levels and mess up your diet.  Snacking on a 250ml can of cola with a crumpet is a massive GL value of 27!  I’ve known many people who drink nothing but cola, having up to 2 litres a day and can’t understand why they feel so ill.

Getting your diet back to basics is crucial if you want to avoid the disease conditions that are almost epidemic in the western world.

Dump white bread, processed foods, biscuits, cakes, cookies, chips.

Instead, eat granary bread, fresh fruit and vegetables, whole grains such as porridge oats, nuts, seeds and good quality proteins.

Having some protein with each meal will slow down the rate at which the sugar content of carbs is released.  Ideally, eat small amounts little and often and take time to enjoy your food and listen to your body when it tells you that it is satisfied by what you’ve eaten. (And then STOP).

This entry was posted in Diet and Nutrition and tagged , , , , , , , , . Bookmark the permalink.

One Response to Low GI or Low GL, what’s the difference?

  1. shirley says:

    This totally works once you get to grips with it, I have ME and this way of eating not only helped me to managed my weight, it allowed me to manage my energy levels through the day, no more ups and downs and feeling starving, I was satisfied and full but light. You don’t have to be totally rigid with it either which was good for me, I wanted to manage energy levels so it was just a case of doing what made me feel good. And Lois explains the difference between GI and GL really well.

    Thanks Lo !!

Leave a Reply