GI and GL made easy

Tina Michelucci of DietFreedom © DietFreedom 2005

GI and GL made easy

To find out the GI (Glyceamic Index) of a food scientists feed volunteers enough of one specific food to give 50g of carbs. For example, if testing bread this would equal two large slices, if testing watermelon, a whole watermelon, or if testing carrots 700 g. They then take blood samples afterwards to see how much each food raises the level of sugar in the blood. GI or Glycaemic Index is the result and is numbered 1 – 100 (low GI equals 55 or less, medium GI 56 - 69 and high GI 70 plus)

Other items of interest

So the GI is a good way, in the science laboratory, to compare the effects of different carbs (i.e. bread carb – v - watermelon carb) but, where it falls down is that it doesn't tell us how much the level of sugar in our blood will rise after we eat a 'normal' portion of the food in quetion. Two large slices of bread are feasible as a portion but how often have you eaten a whole watermelon or 700g of carrots at one sitting? Unless you’re a donkey of course.

Enter GL

GL or Glycaemic Load is a simple calculation based on the GI test result, but importantly, it also takes into account the amount of carbs contained in an average food portion. This gives us a relevant reference that can be directly related to the actual amount of food we eat, which is crucial. For example the GI of watermelon is 72, (a whole one would have been used in tests) so it is classed as a high GI food (anything with a GI over 70 is high) BUT the GL of a 'portion' of watermelon, i.e. a large slice (120g) contains very few carbs and so when you calculate the GL it has a very low score of 4, (a GL score of 10 or less is low).

This means that a normal 'portion' of watermelon will have little or no effect on the level of sugar in your blood – so you should eat and enjoy and not avoid as it is 'high GI'.

Professors from Harvard University (the most prestigious and longest established nutritional research establishment in the world) came up with the GL calculation as they felt that using GI alone as a food reference doesn’t give a true picture, and we couldn’t agree more!

Most authors of GI books are now starting to talk about GL, although The GL Diet and The 7 Day GL Diet were the first to be published.

So you can forget GI

The only reference you need to think about is GL Low GL = 10 or less Medium GL = 11 – 19 High GL = 20 plus Most people have a high GL or Glycaemic Load of over 120 per day from what they eat. Aim for a lower GL of around 80 per day as a good target. A comprehensive food list with GL scores can be found in dietician, Nigel Denby's latest book The 7 Day GL Diet or on the diet freedom website