A banana contains up to 3.1 grams of insoluble fiber. "Insoluble" means the body does not absorb the fiber, but it adds bulk to the digestive tract.
Green bananas contain more fiber than riper fruits because the pulp has not yet been broken down into simple sugars. Before a banana has ripened, its fiber is a resistant starch that remains in the colon and is not dissolved by the small intestines. This gives a person the feeling of fullness, decreases the appetite and could help with weight loss efforts.
A banana contains about 14 grams of sugar and 1.3 grams of protein. One banana also provides 25 percent of the daily recommended value for vitamin B6.