To show how GI should be interpreted (as I understand it) I have made
a little comparison:

Food            GI      %carbs          GI/100g         Portion
White bread     100        50            50             1 slice  = 25 g
Carrot           70        10             7             1 7-8"   = 70 g
Apple            54        15             8             1 medium = 140 g
Banana           70        23            17             1        = 115 g
Pasta         50-65        25            13

From this table we can se that 1 slice white bread will give You
a "glycemic effect" of 13 units. That equals 100 * 13 / 7 = 200 grams
of carrot, or 3 medium sized. If You are hungry and hesitate between
bread and carrots, and eat until You are satisfied, guess the resulting
difference in blood sugar!
Apples to compare with one 25 g bread slice will be one and a half.
Banana will be a little less than one.
Pasta will be 100 grams.
I think it is a sad thing that GI tables don't include this kind of
information, because of the risk of misinterpreting would be reduced.
Saying that carrot is a little bit high in GI is true, but in practice
it is low because of water and fiber content.

- Hans