What is Glycemic Load and how is it different to Glycemic Index?

We’ve all heard a lot about the Glycemic Index (GI) – an index that ranks carbohydrates according to their immediate effect on your blood sugar levels.

But what about the term “Glycemic Load”?  What is it?  How is it different to GI?  And which one am I supposed to refer to?  These are all very good questions!

What is GI?

GI looks at the effect a portion of carbohydrate has on your system right away, so it‘s essentially a measure of the quality of the carbohydrate.  Good quality carbohydrates release energy slowly.  Lower quality carbohydrates produce a sharp spike in your blood sugar levels, followed quickly by an energy slump.

But the GI does have a small flaw – it’s based on a test portion size of 50g of carbohydrate, which is rarely representative of the portion size you’re eating in real life.

For example, watermelon has a GI of 72, which makes is a high GI food.  But there are only 6g of carbohydrate (approximately) in a 120g slice, so you’d have to eat over 6 slices to hit that GI!

This is where Glycemic Load (GL) comes in… it takes into account the size of the portion of carbohydrate you’re actually eating.

And why is GL important?

And why would you want to do that?  Well, GL enhances the concept of GI, so it’s important for 3 very important reasons:

• Controlling blood sugar levels is an important tool in diabetes management
• Avoiding sustained blood sugar spikes can help avoid the onset of type-2 diabetes
• A small to moderate GL helps reduce the storage of fat in the body, and increases glycogen (readily available blood sugar) stores

Ok, how do I go about calculating GL?

The formula is pretty simple, but you need to know the GI of the food you want to calculate GL for, first.  The Glycemic Index Foundation has a fantastic database for this.

Then, the formula is:
GL = (carbohydrates per portion x GI) / 100

In keeping with the watermelon example:
GL = (6 x 72) / 100
GL = 4

That’s pretty easy, but what is a good, moderate, or low level GL?

Low GL foods produce a result between 0 and 10
E.g. wholemeal bread (9), baked beans (7), pitta bread (10) and peanuts (1)

Moderate GL foods are those with a result between 11 and 19
E.g. rice cakes (17), brown rice (18) and bananas (12)

Foods with a high GL are those with a result over 20
E.g. baked potato (26), raisins (28) and white rice (23)

… and finally

The concept of GL only has relevance in relation to GI.

Eating small portions of low GI, low-carbohydrate foods will produce a smaller and more prolonged rise in blood sugar levels (i.e. more stability).  Conversely, eating almost any sized portion of high GI food will produce a sharp surge and subsequent drop in blood sugar levels.

Unfortunately, a diet that’s low in GL doesn’t always equal success because lots of foods, like meat and butter, are low in carbohydrates but high in bad (trans and saturated) fats.

What about incorporating GI/GL into meal planning?  Well, I’d have to echo the Glycemic Index Foundation’s advice and recommend you choose a diet that’s low in healthy GI carbohydrates (to regulate blood sugar levels) but limit the overall diet GL if necessary.

I use a fantastically handy little book called “GI & GL Counter”, which also contains nutritional information for most fresh foods and some pre-packaged / fast foods.  You can pick one up from Amazon - see below for publishing information.

As always, if you have any questions, please ask!

“GI & GL Counter”
Chan, Wynnie, Dr. (2006), Hamlyn, a division of Octopus Publishing Group, London, England