The Glycaemic Index & Glycaemic Load
The index was determined in the following way; after an overnight fast subjects were fed foods that contained 50grams of carbohydrate and the subjects subsequent blood glucose levels were measured. Foods that were deemed to be ‘high GI’ were rapidly digested and absorbed, resulting in a faster and higher rise in blood sugar levels, while foods that were deemed to be ‘low GI’ were slowly digested and absorbed, resulting in a lower rise in blood sugar levels.
It is generally recommended that we eat more low GI foods. This is because they are slower to digest than high GI foods and as a result they provide energy and a sense of fullness over a longer period when compared to high GI foods which give a short burst of energy, and a temporary sense of fullness.
Much like eating carbohydrate foods that are high in fibre, eating low GI carbohydrate foods helps to control bodyweight as theoretically we eat less low GI foods due to the sustained nature of their breakdown, and the prolonged sense of fullness they offer.
As there is a lower response on blood glucose levels with low GI foods people with diabetes are advised to eat low GI to help control their blood sugar levels.
The table below shows the GI ratings of some common foods;
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Glycaemic index (GI) of common foods |
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Low GI (below 55) |
Apples, oranges, oats, barley, legumes, pasta, coarse rye bread, All-bran, natural muesli, breads with a high content of whole grains, seeds and fibre, grapefruit, berry fruits, stone fruits, under ripe bananas, kiwifruit, pears, sweat corn, yams, peas, baked beans, short grain rice, grapes, fruit & vegetable juices, mango’s |
|
Medium GI (55-69) |
New potatoes, white rice, beetroot, melon, pineapple, wheatbix, instant porridge, wholemeal bread, raisins and sultanas, ripe bananas, taro, pita bread, most long grain rice including basmati, pasta, noodles, couscous, popcorn, potato crisp’s/chips |
|
High GI (above 70) |
Most potatoes, parsnip, carrot, highly refined white breads and breads with a high white flour content, watermelon, kumara (sweet potato), dates, broad beans, water crackers, rice cakes, rice crackers, jasmine rice, long cooked white rice, cornflakes, rice bubbles, sultana bran, puffed wheat, rice bubbles (manufactured breakfast cereals) |
|
100 |
Pure glucose/sugar |
While the GI is useful it does have a major limitation as it doesn’t take into account the amount, or ‘quantity’ of food that is consumed during testing in order to provide 50 grams of carbohydrate. Try to remember that carbohydrate is not a food, rather it is a nutrient that is found in lots of different foods, and it is found in these different foods in different concentrations.
For example, sugar (or sucrose) is pure carbohydrate, i.e. 50 grams of sugar provides 50 grams of carbohydrate. In comparison it requires 800 grams of carrots to provide 50 grams of carbohydrate. Watermelon is another example, like carrots it is considered high GI, but only has 5 grams of carbohydrate per 100 grams of total watermelon, so we’d have to eat about 1 kg of it to provide 50 grams of carbohydrate (the rest of the watermelon is just water and fibre).
This is where the glycaemic load (GL) comes into play, as it takes into account the amount of carbohydrate a typical serving of food contains as well as its GI.
Glycaemic load is defined as the amount of carbohydrate in a portion of food multiplied by the GI value for the food, divided by 100.
Consequently some foods that we may have avoided due to being considered high GI are shown to be pretty good when we consider typical serving sizes. For example, how often does anyone really sit down and eat 800 grams of carrots in one go, or 1 kg of watermelon – as that is what is required for those foods to cause the ‘high GI’ effect on a persons blood sugar levels
The following table shows the GL of some common foods including many of those from the glycaemic index above, note how some of these have changed as the total amount of food that is consumed is considered;
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Glycaemic load (GL) of common carbohydrate foods |
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Low GL (below 10) |
Apples, carrots, watermelon, pear, pineapple, peanuts, kidney beans, chick peas, peas, lentils, pop corn, most breads with a high content of wholegrains, seeds and fibre, oranges, stone-fruit, baked beans, butter beans, mung beans, most nuts, pumpkin, taro, unripe banana, kiwifruit, mango’s |
|
Medium GL (10-19) |
Apple juice, orange juice, ripe banana, new potato, kumara (sweet potato), most breads with a high content of white flour, wheatbix, sweet corn, rice cakes, dates, instant noodles, potato crisps |
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High GL (above 20) |
Pasta, couscous, white rice, brown rice, cornflakes, rice bubbles, rice crackers, raisins, sultanas, most potatoes, yam’s, most highly refined white breads with no visible wholegrains, seeds or fibre |
Neither the GI nor the GL however take into account the effect dietary fibre has on digestion. In fact most low GI & low GL foods are also unprocessed high fibre foods, so there is an argument to suggest that the actual benefit of eating low GI and low GL is due to the beneficial effect of fibre.
While the GI and GL certainly have credibility and interest value, in many ways they actually add to the confusion in regard to what is ‘healthy eating’? It would seem that supporting the general message of most national nutrition bodies in regard to eating more fresh fruit and vegetables, wholegrain breads and cereals and legumes is not only credible but much easier for the general population (and your clients) to understand, and therefore much more useful.
