What You Need to Know About the Glycemic Index

The glycemic index or GI is a popular concept used to determine the effect of certain carbohydrates on blood sugar levels in the body. It therefore represents the metabolic response of the body to the carbohydrates we eat, and is classified into 3 groups:


1. Low GI foods = <55 GI value

2. Medium GI foods = 56 – 69 GI value

3. High GI foods = 70 or greater

Foods that have a low GI do not raise blood glucose levels as much, nor as fast as foods that have a high GI. The GI for a particular carbohydrate is primarily dependent on the rate at which the food (and carbohydrate) is digested, thus resulting in how quickly glucose appears in the blood stream.

The GI index ranking is based on a standard food such as white bread or pure glucose which is given the arbitrary GI of 100. To work out the GI of a particular carbohydrate, the carbohydrates 2-hour glucose response curve is compared with 50g of carbohydrates from the control food i.e. white bread or glucose.

There are a number of important factors that will affect the digestion rate of a carbohydrate, namely: the type of carbohydrate, the amount, fibre content and proportion of other macronutrients present.

The initial decision to create the GI was based on the studies showing that unstable (rising and falling) blood sugar responses to food are linked with poorer health outcomes e.g. insulin-resistance, prediabetes and diabetes. Recent research however, shows no correlation between the GI of a food and cardiovascular diseases but it is a great tool to highlight how various carbohydrates will impact blood sugar levels and how the body may respond based on this.

Below is a table listing common carbohydrates and their respective GI:

The glycemic index, or GI, is a measure used to determine how much a food can affect your blood sugar levels.

Several factors affect the glycemic index of a food, including the nutrient composition, ripeness, cooking method, and amount of processing it has undergone. 

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