GI - what a load of...

GI. Joe.

Glycaemic index.  In scientific lingo what the glycaemic index is = the area under the blood glucose curve over a two hour period in response to consuming a test food providing 50g of glycaemic carbohydrate which is compared to a 50g sample of a reference food.  The reference food being glucose or white bread. These foods are expressed on a scale of 100. Or something like that.  In brick layer chat this means how much a food effects your blood sugar levels. Or does it?

The glycaemic effect of a food or how much it affects your blood sugar is influenced by the type of carbohydrate present, as well as the presence of fat, fibre or protein in the food or what other food is being eaten at the same time.  Add to this the acidity and temperature of the food item, how refined it is, it’s ripeness, it’s variety and how much you have chewed it and you may have a number of different factors affecting glycaemic responses.  Then throw in there the fact that this slice of brown bread was made with 50% white flour, but the one I had yesterday was 100% unrefined.  Or that today I boiled my potato but yesterday it was baked.  All of these factors give us absorbable carbohydrates at a different rate.

 

Why is this control of blood glucose important anyway? Well for general health we want to avoid highs and lows in our blood glucose levels to prevent a loss in insulin sensitivity.  Insulin is the hormone the controls glucose levels amongst other things, without it we are diabetic and that is not a great place to be. We also struggle to control body composition with these fluctuations and our hunger cues are linked to our glucose levels.  So too are hydration, heart rate and cognitive (brain) function.  For an athlete you want the right type of carbohydrate at the right time, either a quick or slow releasing carb.  With these goals in mind some spark decided to test a few foods on a few people and see how they fared compared to white bread or glucose.

First problem: there are two scales of GI, one uses white bread, the other uses glucose.  There are arguments to pros and cons of using a different reference food, but mainly confusion.  On the white bread scale all foods have a higher GI than on the glucose scale.

Next: not all foods that are given a GI rating are tested. They are merely estimates according to their ingredients.  And what about all the factors like ripeness, variety, cooking method etc etc..

Then only small samples of people are needed to provide a GI value for a food, the number is 10. This somehow provides us with a consensus on how 6 billion people would react to a food when compared to white bread..or glucose..

An example of a high glycaemic index food: watermelon has a GI of 96 (I don’t know which scale this is). You would think that watermelon would have so much sugar in it because it got an A+ in the GI exam.  You know how much you would have to eat for it to affect your sugar at all! Most of it is water, it is not called sugar melon. To provide the 50g of sugar necessary for the test you would have to eat about 900g of the stuff.

Anyway if we were to follow the GI route and believe its value then perhaps the slightly more relevant scale of glycaemic load (GL) is worthwhile.  This takes into account the GI of a food and the amount of carbs in a portion that you would actually eat. We don’t hear too much about GL though. 

I am not saying we should ignore the value of understanding how foods affect us but I dont agree this is the way.  Knowing which foods provide quick releasing, simple sugars is quite easy to figure without the mystical GI.  High fibre foods or those containing fats and protein are not quick releasing.  Foods with a lot of water or other non-carbohydrate ingredients can’t have too much available sugar in an average portion.  Sugary and sweetened foods and drinks, refined grains and a few fruits like bananas, grapes and peaches are quick releasing.

So for everyone out there choose the high fibre, slow releasing foods for most snacks and meals.  Wholegrains, vegetables, legumes and fruit should be predominant.  The quick releasing sugar foods are only really valuable before, during or after exercise or when you feel like a little treat.  A diet high in added sugars and refined carbohydrates are strongly linked to obesity, diabetes and cardiovascular disease.  There is no point in giving these foods an arbitrary number that means you might miss out on valuable food options because they have been wrongly classified.  Don’t fall for the gimmicky low GI labels, read the ingredients and make your own choices.  A fibre content of at least 5g per 100g is a guide and the ingredients list is in order of quantity, most to least. Learn what the labels on food mean!

G bye.