However, a standard serving of food may not contain 50 grams of carbohydrate. For example, watermelon has a very high glycemic index of 72, but contains only 5 percent carbohydrate by weight. Most of watermelon’s weight is water. You would need to eat 1 kilogram (2.2 pounds!) of watermelon to get 50 grams of carbohydrate—far in excess of what a person would eat at one sitting.
