This is a way of measuring how the food that you eat affects the amount of sugar in your blood. This is important for a number of reasons.
A food with a GI value of 55 or less is labelled “Low GI”. The food will have a slower, longer impact on you, energy-wise. High GI foods (those with a GI above 70) will be used by your body before any stored energy like body fat. And this may make weight loss more difficult.
French Baguette - 95
Bagel - 72
White Bread - 71
Croissant - 67
Wholemeal Rye - 62
Hamburger Bun - 61
Pitta - 57
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Sourdough Wheat - 54
Whole Wheat - 49
Sourdough Rye - 48
Pumpernickel - 46
Heavy Mixed Grain - 45
Soya and Linseed - 36
Source
http://www.the-gi-diet.org/lowgifoods/