High-glycemic carbohydrates are found in foods with simple sugars or foods easily broken down into simple sugars, which includes cereals, white bread, potatoes and crackers. Most fresh fruits are low or moderate on the glycemic index, but some are significantly high on the scale.
The glycemic index is a measure of how high a food containing carbohydrates raises a person's blood glucose after eating it. Foods high on the glycemic index raise blood glucose higher than foods on the low end of the index. Foods are compared to a reference food for this rating, usually simple glucose or plain white bread.
White rice, russet potatoes, white bread, cereal and crackers are all at the top of the glycemic index. Some fruits are also high, such as watermelon, cantaloupe and pineapple. Foods that contain a lot of added sugar especially rank at the top of the glycemic index, such as sodas, candy bars and many fruit juices.
Foods that have more fiber and fat are usually lower on the glycemic index, while processed foods tend to be higher because it takes less work for the body to break down processed foods into the simple glucose it needs. Foods with more fiber or fat require the body to put forth more effort to get the glucose it needs, raising blood glucose levels much less.