Yellow During ripening, the starch in a banana is converted into sugar — from 3.2g/100g in an unripe banana to 12g/100g in a ripe one. ‘This is what makes them a good source of quick release energy for athletes,’ says dietitian Dr Sarah Schenker. The lower quantities of resistant starch also means yellow bananas are easier to digest. If you have digestive problems, green bananas can leave you feeling gassy or bloated. Dr Schenker suggests the health benefits of yellow bananas trump those of green ones.