Its role is to supplement blood glucose levels if they drop between meals especially overnight or during physical activity. The glycaemic index GI is a way of ranking carbohydrate-containing foods based on how slowly or quickly they are digested and increase blood glucose levels over a period of time — usually 2 hours.

The GI uses glucose or white bread as a reference food — it has a GI score of Carbohydrate-containing foods are then compared with this reference to assign their GI. This ensures all foods compared have the same amount of carbohydrate, gram for gram.

Carbohydrates that break down quickly during digestion have a higher glycaemic index. These high GI carbohydrates, such as a baked potato, release their glucose into the blood quickly. Carbohydrates that break down slowly, such as oats, release glucose gradually into the bloodstream.

They have low glycaemic indexes. The blood glucose response is slower and flatter. Low GI foods prolong digestion due to their slow breakdown and may help with feeling full. These ranges, along with some example foods, include:. For instance, although both ripe and unripe bananas have a low GI less than 55 , an unripe banana may have a GI of 30, while a ripe banana has a GI of Fat and acid foods like vinegar, lemon juice or acidic fruit slow the rate at which the stomach empties and slow the rate of digestion, resulting in a lower GI.

Cooking and processing can also affect the GI — food that is broken down into fine or smaller particles will be more easily absorbed and so has a higher GI.

Foods that have been cooked and allowed to cool potatoes, for example can have a lower GI when eaten cold than when hot for example, potato salad compared with hot baked potato. This is important, as most foods are eaten as part of a meal and this affects the GI value of foods. For example, eating cornflakes a higher GI food with milk a lower GI food will reduce the overall effect of the cornflakes and milk meal on blood glucose levels.

These are examples of nutrition content claims and general level health claims, allowed by Food Standards Australia New Zealand under Standard 1.

The Low GI Symbol and claims about the relationship of a low GI product and its effect on health is only available to packaged food products that meet strict nutritional and testing criteria. This labelling is not compulsory for food companies to follow, so not all products that are eligible will display the symbol or make a claim.

This is often the case for smaller companies who may not have the money to go through the necessary processes to be given the label. The amount of the carbohydrate-containing food you eat affects your blood glucose levels.

For example, even though pasta has a low GI, a large serving can still cause the blood glucose levels to rise more rapidly than a smaller serving. This is what is called the glycaemic load GL.

The GL builds on GI, as it considers both the GI of the food and the amount of carbohydrate in a portion. GL is based on the idea that a high GI food consumed in small quantities would give the same effect on blood glucose levels as larger quantities of a low GI food.

The GL calculation is: GI x the amount of carbohydrates in grams in a serving of food ÷ Using a pasta example:. Here is another example, where both foods contain the same amount of carbohydrate but their GIs are different:.

Both the small baked potato and the apple have the same amount of carbohydrate 15g. However, because their GIs differ the apple is low while the baked potato is high , their GLs also differ, which means the baked potato will cause the blood glucose level of the person eating it to rise more quickly than the apple.

Eating low GI foods 2 hours before endurance events, such as long-distance running, may improve exercise capacity. Moderate to high GI foods may be most beneficial during the first 24 hours of recovery after an event to rapidly replenish muscle fuel stores glycogen. This tool measures how much a food boosts blood sugar.

The glycemic index rates the effect of a specific amount of a food on blood sugar compared with the same amount of pure glucose. One with a GI of 95 acts like pure glucose. High glycemic foods result in a quick spike in insulin and blood sugar also known as blood glucose.

Low glycemic foods have a slower, smaller effect. Using the glycemic index is easy: choose foods in the low GI category instead of those in the high GI category see below , and go easy on those in between. Associations of glycemic index and load with coronary heart disease events: a systematic review and meta-analysis of prospective cohorts.

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Atkinson FS, Foster-Powell K, Brand-Miller JC. International tables of glycemic index and glycemic load values: Donate to the MIC. Get Updates from the Institute. The Linus Pauling Institute's Micronutrient Information Center provides scientific information on the health aspects of dietary factors and supplements, food, and beverages for the general public.

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