Glycaemic index?

Low GI, what does that mean?

Sugar in the blood (called blood glucose) powers the body, providing the brain, muscles and other tissues with the energy they need. But if blood glucose levels rise too high, they can harm various body organs – as happens in diabetes, a disease marked by high blood glucose concentrations.

Diabetes is quickly becoming one of the world’s most common plague, and every person needs to choose a lifestyle that will minimise his or her risk of developing diabetes. The cornerstone of a healthy lifestyle is a healthy diet that keeps blood glucose levels within the normal range and helps maintain a healthy body weight. It is therefore extremely helpful to know how the foods we eat affect our blood glucose levels.

To provide consumers with an easy – or, shall we say, “short and sweet” – measure of the way your blood glucose levels are affected by the consumption of different foods, nutrition scientists have devised the concepts of the glycaemic index (GI) and the glycaemic load (GL). While neither offers a perfect way of assessing the effects of food on blood glucose levels, you might encounter the GI on food labels and should therefore know what they mean.

What is the glycaemic index?

The glycaemic index, or GI, reflects the effect of different carbohydrate-containing foods – starches, sugars, fruit and vegetables, snacks and soft drinks – on blood glucose levels. Dairy products might also have a glycaemic index.

On a scale of 0 to 100, the GI of different foods can be rated as low (less than 55), medium (55 to 70) or high (higher than 70). The impact on blood glucose levels varies depending on the GI value:

·         Foods rated as having a low GI score, like raw oat bran or fat free milk, can be eaten with a minimal effect on blood glucose levels.

·         Foods considered medium, like fruit bran cereals or canned sweet corn, result in a medium blood glucose response.

·         Finally, foods rated as having a high GI, like instant oats or wafer biscuits, are expected to result in raised blood glucose levels.

How is the glycaemic index calculated?

The glycaemic index is a relative measure: it shows how a certain food compares to the two reference foods of the blood glucose world: pure glucose and white bread. To establish the GI, researchers assemble a group of study participants, measure their blood glucose response to 50 grams of various carbohydrate-containing foods and compare these to the responses obtained in the same people with 50 grams of pure glucose or white bread. All the results are plotted on a graph, in which the GI of pure glucose is defined as 100 and that of white bread as 70. Each of the tested foods is then assigned its own GI, depending on its curve drawn on the graph.

What the glycaemic index is NOT

Be careful not to get too sweet on the glycaemic index! Though it is a catchy and convenient measure, it has its limitations.

First of all, the GI is not foolproof and you should not use it as your main measure in making dietary choices.

Another word of caution: do not confuse foods having a low GI with low-energy foods recommended for weight loss. The GI is only a relative measure of how the food affects blood glucose – it says nothing at all about the inherent kilojoule content of the food.

Finally, the GI of a food reflects the ‘glucose responsiveness’ of its carbohydrates, but it tells you nothing about the quantity of carbohydrates it contains. Obviously, however, the effects of a teaspoon of sugar cannot be compared with the sugar assault delivered by an entire packet of sweets!

What is the difference between Glycaemic index and Glycaemic load?

To address the latter problem of the glycaemic index failing to take the quantity of carbohydrates into account, the same scientists have designed an additional measure called the glycaemic load (GL). It is calculated by multiplying the glycaemic index of a certain food by the amount of carbohydrates contained in a particular portion of this food, divided by 100.

For example, the glycaemic index of table sugar is 60, but its glycaemic load varies depending on how much sugar you use. Therefore, the glycaemic load of a teaspoon of sugar, or 5 grams, is 3.3, but for a 100-gram packet of sweets, the load is a whopping 65!

The concept of the glycaemic load helps avert the misleading impression sometimes created by the glycaemic index. For example, that the glycaemic index of carrots is 70, while that of sugar is 60 and that of spaghetti is 40.

Beware of anyone who will try to use these numbers to explain to you that sugar can be eaten in large amounts, or a big bowl of spaghetti is better than carrots for managing blood glucose levels! The glycaemic load helps to set things straight: since carrots contain relatively few carbohydrates, the glycaemic load of 50 grams of carrots is only 2, while 50 grams of sugar carry a glycaemic load of 30 and 50 grams of spaghetti, 19!

Different factors affect the glycaemic index

The glycaemic index is increased by processing and refinement and decreased by the presence of dietary fibre (the soluble, viscous kind not the insoluble bran added to bread and cereals). The type of starch present in the food will also affect the GI.

Cooking, as well as the chosen method of cooking, affects the GI, for example a baked potato has a lower GI than a boiled potato, but mashing a boiled potato will further disrupt the starch granule therefore increasing the GI.  Lastly, combining carbohydrates with protein and fat lowers the GI of a meal, so white bread alone will have a higher GI than bread with tuna and mayonnaise.

The many factors that can and do affect the GI of foods clearly illustrate that the GI is not as short, sweet or as easy to implement as initially thought, and most importantly while it examines how blood glucose responds to carbohydrate containing foods, it does not examine the insulin response that follows, which is the other half of the equation.

Examples of the glycaemic index of food



Low GI (< 55)

Medium GI (55 – 70)

High GI (> 70)


Low-fat, fat-free and plain yogurt


Flavoured yogurt


Whole-wheat and oat-based cereals and high fibre bran cereals

Oats, raw and cooked, sugar frosted cereals and shredded wheat

Instant oats and maize or wheat-based cereals e.g. cornflakes, Weetbix

Bread and flour

Wholegrain or mixed grain breads e.g. granary, rye bread

Pita bread, Crumpet

All brown, white and regular wholemeal bread

Starchy foods

New potatoes in their skins, Basmati rice

French fries (hot chips), boiled old potatoes, white and brown rice

Potatoes –baked/jacket, mashed, and instant mash potato


Apple, pear, plums and all citrus fruit

Tropical fruit e.g. banana, mango, pawpaw, apricots, peaches

Fruit juices, lychees watermelon

Beans and pulses

All legumes i.e. dried, cooked and canned beans, lentils and peas




All green and salad vegetables, carrots

Sweet corn, beetroot,

Parsnip, pumpkin

In summary

·         The concepts of the glycaemic index and glycaemic load provide unique insights into how carbohydrates affect our blood glucose levels.

·         Both concepts have their limitations; avoid using them as your main or only consideration in making dietary choices.

·         The glycaemic index can be misleading as it doesn’t take carbohydrate quantity into account; the glycaemic load is a better measure in this respect.

·         There is even variability in how an individual responds to the reference food of glucose or white bread

·         The GI of the same food differs by country. Ensure that the GI score is for the food that you will be eating.

Source: Vitality Health


About Shaun That Awesome Guy

Husband to the most beautiful woman, Man of honour, Gym enthusiast, Artist, Man of Steel, That Awesome Guy.
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