Bananas are an excellent source of potassium and supply vitamin B6, fibre and carbohydrate, and some vitamin C. Since they have a lower water content than most fruit, bananas typically have more calories as well as a higher sugar content compared to other non-tropical fruits.
A 100g serving provides 81kcal, 20.3g of carbohydrate, 1.4g fibre and 18.1g of natural sugar.
Unripe bananas have a higher starch content. As they ripen, the starch is converted to sugar (and the fruit becomes sweeter). Green bananas are also a good source of pectin, which is a type of dietary fibre found in fruits and helps them keep their structural form. Pectin breaks down when a banana becomes overripe, which causes the fruit to become softer.