What Is The Glycemic Index All About Anyway?

We all know about counting carbs and watching our fat intake, but monitoring the Glycemic Index of Foods is becoming more important.  Especially if you're looking to get lean and #buildmuscle.  Low GI Foods like whole wheat bread take longer for the body to breakdown, whereas high GI foods like white bread are digested quickly.  The higher the Glycemic Index, the greater the chances of having your blood sugar spike. So what is the Glycemic Index?