The glycemic index measures how quickly food affects your blood sugar. When blood sugar rises quickly, the pancreas sends out insulin which enters the bloodstream. Insulin's job is to escort excess sugar out of the bloodstream. Foods that make your blood sugar rise quickly are high-glycemic foods.
High-glycemic foods that you should avoid are processed carbohydrates and those with a high sugar content. Even whole grain products, thought to be so important for good health, can be high-glycemic foods.
Too much sugar increases the chance of getting heart disease. Fat is not the problem. To protect your health, avoid eating too much sugar.
"This study reinforces what I- and many of my colleagues- have been saying for years: Stop worrying so much about fat and start paying attention to sugar. If you consume a reasonable calorie diet (target weight x 10-12 for calorie goal), and get most of your carbs from low-glycemic vegetables and fruits, the percentage of fat in the diet doesn’t matter nearly as much as you might think."
http://www.healthiertalk.com/can-carbs-kill-you-hidden-danger-bread-pasta-and-rice-1796