What is the glycemic index used for and how did it come about?

Firstly the glycemic index was developed as an easy reference tool for measuring out of a score of 100 which foods raise blood sugar. The raising of blood sugar leads to the pancreas secreting the hormone insulin to control excess sugar in your blood stream.
Excess blood sugar is basically the main bio marker in diabetes. The scourge of the western diets and probably the main cause of obesity and the associated diseases.

Now to verify what I am saying I would like you to google "glycemic index of foods". Check out two slices of bread. Forget whether it is "healthy whole grains" (a brilliant marketing strategy),white bread or any other type of bread. Comes up around 70. Now do the same thing with a snickers bar. Around 59. Yes, you saw right. Two slices of bread raises blood sugar much higher than a snickers bar!

Now don't get me wrong. I am not talking about replacing bread with snickers bars. Makes sense obviously.

What I am saying and it is proven by the number of people I have told to drastically reduce their bread (and pasta,rice and potatoes) which are high in carbohydrates with non or low insulin spiking foods like eggs, meat,fish,nuts just to name a few.