One cup of sliced bananas has 18 grams of sugar, which is more sugar than 1 cup of other popular fruits. In comparison, a cup of blackberries has only 7 grams of sugar, strawberries 8 grams and apples 13 grams. One cup of grapes, however, contains 23 grams of sugar.
The amount of sugar in 1 cup of bananas is slightly higher, but comparable to, pineapples, which have 16 grams of sugar in one cup, and sliced oranges, which have 17 grams of sugar. While the U.S. Department of Agriculture advises people to consume two servings of fruit each day, those who are on sugar-restricted diets should stick with fresh or frozen fruit, as canned fruits and fruit juices have a considerable amount of sugar added.