Nutritional Profile. Bananas are a very good source of vitamin B6 and a good source of manganese, vitamin C, potassium, dietary fiber, potassium, biotin, and copper. Bananas are a good source of potassium, an essential mineral for maintaining normal blood pressure and heart function. Fiber is a nutrient that helps regulate the speed of digestion, and by keeping digestion well-regulated, conversion of carbohydrates to simple sugars and release of simple sugars from digesting foods also stays well-regulated.