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Glycaemic Index or Glycaemic Load - what's the difference? [article]

There is a difference between glycaemic index and glycaemic load but as you'll see from this article, the interest in the glycaemic index may be preventing the key messages getting through!

Glycaemic Index or Glycaemic load – What’s the difference?

 

As the debate over carbohydrates (are they good or bad, what do they do, when can you not eat them) intensifies, the glycaemic index (GI), and glycaemic load (GL) have gained credibility as tools to help explain the effect carbohydrate foods have on the body, and thus which to avoid, and which to eat. 

 

The glycaemic index is a ranking of carbohydrate foods based on the effect they have on blood glucose levels after consumption.  After an overnight fast subjects are fed foods that contain 50grams of carbohydrate and their subsequent blood glucose levels are measured.  Foods that are deemed high GI are rapidly digested and absorbed, resulting in a greater rise in blood sugar levels, while foods deemed low GI are slowly digested and absorbed resulting in a lower rise in blood sugar levels.

 

It is generally recommended that we eat more low GI foods as due to a slower digestion they will provide energy over a longer period than high GI foods which give a short burst of energy.  Eating low GI helps weight control as theoretically we eat less low GI foods due to the sustained nature of their breakdown.  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;

 

Glycaemic index (GI) of common foods

Low GI

(below 55)

Apples, oranges, oats, barley, legumes, pasta, coarse rye bread, All-bran, natural muesli, breads with 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, burgen bread, mango

Medium GI

(55-69)

New potatoes, white rice, beetroot, melon, pineapple, wheatbix, instant porridge, wholemeal bread, raisins and sultanas, very ripe bananas, taro, nutragrain, pita bread, most long grain rice including basmati, pasta, noodles, cous-cous, popcorn, vogels bread, potato crisps

High GI

(above 70)

Most potatoes, parsnip, carrot, white breads, watermelon, kumara, dates, broad beans, water crackers, rice cakes, rice crackers, jasmine rice, long cooked white rice, cornflakes, rice bubbles,  molenburg bread and other grain breads with high white flour content, sultana bran, puffed wheat, rice bubbles

100

Pure glucose/sugar

 

While the GI is useful it does have a major limitation as it doesn’t take into account the quantity of food consumed for testing in order to provide 50 grams of carbohydrate. Confused? Lets’ explain it basically. Carbohydrate is not a food per se, it is a nutrient 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 it provides 50 grams of carbohydrate, and 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, so we’d have to eat about 1 kg of it to provide 50 grams of carbohydrate (the rest is really just water and fibre). 

 

This is where the glycaemic load (GL) comes into play, as it takes into account how much 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 high GI are shown to actually be not that bad 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 blood sugar levels 

 

The table below shows the GL of some common foods including many of those from above, note how some have changed as the amount of food is considered;  

 

Glycaemic load (GL) of common foods

Low GL

(below 10)

Apples, carrots, watermelon, pear, pineapple, peanuts, kidney beans, chick peas, peas, lentils, pop corn, vogel’s bread, burgan bread,  oranges, stone-fruit, baked beans, butter beans, mung beans, most nuts, pumpkin, taro, unripe banana, kiwifruit, mango

Medium GL

(10-19)

Apple juice, orange juice, ripe banana, new potato, kumara, molenburg bread, weet-bix, sweet corn, rice cakes, dates, instant noodles, potato crisps,  

High GL

(above 20)

Pasta, cous-cous, white rice, brown rice, cornflakes, rice bubbles, rice crackers, raisins, sultanas, most potatoes, yam

 

A comprehensive listing of the GI & GL of many foods

 

Neither the GI nor the GL take into account the effect of fibre.  Dietary fibre is found in fruit, vegetables, legumes and many cereals, it adds bulk to meals without calories, making us feel full, as well as slowing the process of digestion.  Many low GI & low GL foods are also 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 effect of fibre and not the glycaemic effect on blood sugar levels.

 

While the GI and GL certainly have credibility and interest value, in many ways they actually add to the confusion in regard to what ‘healthy eating’ is. It would seem that supporting the general message from the New Zealand Ministry of Health in regard to eating more fresh fruit and vegetables, wholegrain foods and legumes such as beans, lentils and peas, is not only credible but much easier for the general population to understand, and therefore much more useful. 

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