What is the Glycaemic Index (GI)?

The Glycaemic Index (GI) is a method of categorising foods according to their effect on blood sugar.

High GI foods are digested and absorbed rapidly and therefore have a rapid and dramatic effect on the blood glucose level, while low GI foods take longer to digest and be absorbed and therefore tend to raise the blood sugar more slowly and maintain it for longer.

The way in which the GI is measured is quite a finicky process, but in a nutshell… Foods are compared to glucose which has a GI of 100, which is the highest possible GI.

Foods are categorised as follows:

• High GI: 70-100
• Medium GI: 56-69
• Low GI: 55 or less

Naturally, foods with lower GI’s tend to keep energy levels stable for longer and will keep you feeling fuller for longer. Low GI foods do not cause large fluctuations in blood sugar levels. This is especially helpful in people with diabetes but is also beneficial to everyone who wants to prevent the feelings of fatigue and drowsiness that seem to set in an hour or so after eating a sugar-rich meal.

What is Glycaemic Load (GL)?

Glycaemic Load (GL) is a measure which considers both the Glycaemic index of a food as well as the total carbohydrate content (amount you would eat at a time) – both of which have a significant effect on blood sugar levels.

Glycaemic Load (GL) = Glycaemic index (GI) multiplied by Carbohydrate content in grams (g) divided by 100.

Your blood sugar level will rise rapidly after a meal with a high GL. It is better to choose foods that are both low GI and low GL where possible to encourage stable blood sugar and sustained energy release throughout the day – these foods are generally called ‘low carbohydrate-density foods’.

What this means, is that they contain less sugar-releasing carbohydrate per gram than other foods. A diet that is rich in low carbohydrate-density foods will promote weight loss and have numerous health benefits like blood sugar control, improved hormone balance and even longevity.

If you are the type of person who likes to measure things and work with numbers – aim for a total daily GL of 100 or less. This means that if you have 3 meals a day, the GL of each meal should be no more than 30.

Choosing foods based on GI and GL:

A colour-coded system is used by dieticians and nutritionists when explaining GI and GL. This is a useful classification because it helps you remember that particular foods are RED and therefore should be AVOIDED.

You will however notice that there are some decent, healthy foods in the yellow column... some of these foods may have a high-GI, like certain fruits, but they contain water and fibre, which means their GL is relatively low. You can certainly enjoy these foods, but just be careful of portion size.

You will also notice that some foods, which you might have considered quite healthy (like a dried-fruit health bar) are actually high-GL.

It is always important to READ FOOD LABELS, and look carefully at the sugar content of foods. Try to stick to LESS THAN 10g sugar/100g of any food you buy - that way you can be assured you will be eating low-carbohydrate-density foods.

What affects GI and GL?

The GI of a food is measured for each specific food as if it were eaten on its own.

However, we rarely eat meals comprised of only one food.  Instead, we eat foods in combinations.  You must understand that the GI of the WHOLE meal or snack is more important than the GI of each food item in isolation.

You don’t NEED to avoid high-GI foods, but it is advisable to eat smaller quantities of these foods.  High-GI foods are not always unhealthy.  And low-GI foods are not always healthy.  Remember to think of the additional nutritional value and benefit your body will derive from eating the foods you choose.

Combining low-GI foods (vegetables, fruits, proteins) with higher-GI foods will reduce the overall GI (and GL) of your meal.

The GI of your meal can be affected by numerous factors:

Ripeness of fruit and vegetables:  As fresh produce ripens, more natural sugars form and the GI of the fruit or vegetable will increase.

Processing, preparation and cooking methods:  Juicing or blending increases the GI as fibre is removed or broken down.  Heating starches, and then allowing them to cool completely lowers GI through the formation of stronger chemical bonds between starch molecules.

Fat content:  Adding any fat to your food lowers the overall GI.  That’s why chocolate has a low GI despite a relatively high sugar content.

Protein content:  Protein takes longer to digest and requires a lot more digestive effort than any of the other food groups.  Adding protein to your meal will reduce the overall GI.

Try to include more low-GI foods whenever possible because these foods tend to keep you feeling fuller for longer, and generally contain more beneficial nutrients.

Below is a table showing GI and GL of many common foods and drinks: