Glycaemic load and what it means for your waistline

What is the glycaemic load?

The glycaemic load (GL) is a measure of both the quality and quantity of carbohydrates, and it incorporates the glycaemic index (GI) but adjusts it for serving size. In case you're unsure, the GI is a ranking out of 100 of how fast a food can raise your blood sugar levels (and therefore it's potential to trigger the release of the fat-storing hormone insulin).

Foods that lead to a rapid rise in blood sugar have a high GI (scored as 70 or more), and are more likely to trigger the release of insulin. Foods that lead to a slower rise in blood sugar are said to have a low GI (scored as 55 or less), and are less likely to trigger the release of insulin.

Foods with a GI of between 56 and 69 have a medium GI. The GL takes the GI into account, but gives a more complete picture of how a food affects your blood sugar levels by considering the portion size. The GL is calculated by multiplying the GI of a food by the available carbohydrate content (carbohydrate minus fibre) in the serving (expressed in grams), divided by 100. Click here* to see the GI and GL scores of over 750 different foods.

Why not just use the GI?

To calculate the GI, test subjects are given enough of a food so they get 50 grams of carbohydrate. The changes in their blood sugars are measured over set intervals of time, and the food is given a score out of 100 based on the average blood sugar changes.

For example, subjects would have to eat about 1 cup of spaghetti (which is a fairly normal serving) to get 50 grams of carbohydrate. On the other hand, subjects have to eat approximately 7 large carrots to get 50 grams of carbohydrate, because carrots contain lots of water and indigestible fibre. Yet spaghetti (64) has a lower GI than carrots (68), and no wonder when you consider the glucose rush that would occur after eating 7 large carrots.

This is where the glycaemic index can be misleading, because the amounts of food test subjects are fed to get GI measurements don’t always reflect the amount people normally eat.
The GL eliminates any confusion and gives fruit and vegetables a much healthier ranking than the GI when compared to more refined carbohydrate foods. For example, one carrot has a GL of 11, while 1 cup of spaghetti has a GL of 166.

The research

In 2009, an American journal reported on a study on over 8000 Spanish adults comparing the effects of low GI and low GL diets. The researchers found that GL had an association with reduced BMI (a marker of body fatness), yet the GI did not have an association with BMI.

The researchers noted that because the GL takes into account the amount and the quality of carbohydrates, foods such as fruits, vegetables, and legumes differed substantially in their scores between the two measures.

It’s interesting to note that fruits, vegetables, and legumes would be likely to feature heavily in the diet of people living in a Mediterranean country such as Spain, which may help explain the differences in GL and GI in this study.

How to lower your glycaemic load

The GI is still a useful measure of carbohydrate quality, and eating lower GI foods will help to lower the GL of your diet. But the additional focus on portion size can have potential weight loss benefits. Follow the tips below to help reduce the GL of your diet.

• Increase the proportion of fruits, vegetables and legumes in your diet compared to other foods
• Cut back on your portion size of starchy, processed carbohydrates like white bread and white rice
• Use other foods, such as protein and healthy plant fats such as nuts, seeds, avocado and olive oil to slow down the absorption of starchy carbohydrates
• Eat pasta al dente (just cooked), and eat it in moderation
• Cut out sugar laden drinks such as soft drink, fruit juice and energy drinks

References available on request