Glycemic this and glycemic that. Does it matter?
In general, diets that are high on the glycemic index (GI) and high in glycemic load (GL), tend to increase the risk of diabetes and heart disease.
FUN FACT: Starches like those in potatoes and grains are digested into sugar; this is because starch is just a bunch of sugars linked together. Digestive enzymes break those bonds so that the sugars become free. Then those sugars affect your body the same way that eating sugary foods do.
Glycemic Index ("how fast")
The most common of the two terms is "glycemic index" (GI).
As the name suggests, it "indexes" (or compares) the effect that different foods have on your blood sugar level. Then each food is given a score from 0 (no effect on blood sugar) to 100 (big effect on blood sugar). Foods that cause a FAST increase in blood sugar have a high GI. That is because the sugar in them is quickly processed by your digestive system and absorbed into your blood. They cause a "spike" in your blood sugar.
So, you can probably guess that pure glucose is given a GI rating of 100. On the other hand, chickpeas are right down there at a GI of 10.
Regarding GI: low is anything under 55, moderate is 56-69, and 70+ is considered a high GI.