Glycemic Index

Eating High GI(Glycemic Index) foods all the time=risk for diabetes, can make you fat, and causes drowsiness during the sugar crash after eating these foods
GI=100=bad
GI=0=good

Table borrowed from Wikipedia

The glycemic index is a scale used to explain how much a food affects your blood sugar.  The higher GI a food has, the more quickly it raises your blood sugar.  Pure sugar has a rating of 100 and things like lettuce and avocado have 0.

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Diabetes and obesity have become enough of a problem that there is now a GI symbol in Australia to help consumers know the risks of certain foods and make better choices.
GI Symbol