More and more nutritionists insist that, just as fats are now broken out into good fats and bad fats, that carbs should be listed as healthy carbs and unhealthy carbs. These numbers are the glycemic index and glycemic load.
In essence, the reason most low carb diets emphasize a reduction of carb intake is that carbs cause the blood sugar to spike high. This tells the body "you have excess calories - turn it into fat". The sugar goes right into fat cells for storage. However, when the blood sugar level drops a short while later, the body doesn't convert quickly enough into fat-burning mode and therefore feels hungry again.
Think of it as the classic "eating Chinese food" syndrome. You eat food coated in sugar and bread, and a lot of white rice. Your body is hit with all this sugar and instantly starts putting it all away into fat cells. But a short time later, instead of using those fat cells for energy when the blood sugar levels drop again, it sends out more "I'm hungry!!" signals. So actually eating a high carb diet encourages your body to keep feeling hungry.
The glycemic index of a food indicates how fast it causes your blood sugar to spike. White bread, for example, has a high glycemic index. Eating white bread causes your blood sugar levels to soar. But eating a tuna steak is very low glycemic. It doesn't cause your blood sugar levels to jump around, meaning your fat burning and satisfaction levels are nice and even.
If you combine the glycemic index of a food with its actual carb count, you get its glycemic load. A carrot for example has a high glycemic index for the carbs in it - but there are hardly any carbs IN a carrot. So its overall glycemic load is low. On the other hand a potato has a high glycemic index AND it has tons of carbs. So its glycemic load is extremely high.
Nutritionists are hoping that by providing the glycemic index and glycemic load information on food items, that people can choose to eat more healthy foods without having to research every food item manually. Just as people now avoid trans fats as being very dangerous, nutritionists are hoping that people will soon avoid high glycemic load foods as being equally dangerous.
Glycemic Index - Definition
Glycemic Load - Definition
Study Shows how Carbs keep you Hungry
Lisa Shea's Library of Low Carb Books