Carbohydrates are a source of energy for your body. Cantaloupes contain about 8 percent carbohydrate. A medium cantaloupe contains 4.6 grams of protein, 1 gram of fat and 45 grams of carbohydrate, and a 1-cup serving of cantaloupe cubes contains 1.3 grams of protein, 0.3 gram of fat and 13 grams of carbohydrate. Sugars are considered simple carbohydrates, as they contain only one or two molecules joined together.