Bananas are one of the most popular fruits in the world. They're full of important nutrients, but eating too many could end up doing more harm than good. Too much of any single food may contribute to weight gain and nutrient deficiencies. Bananas are a good source of several vitamins and minerals, especially potassium, vitamin B6, and vitamin C. Potassium. Bananas are a good source of potassium. A diet high in potassium can lower blood pressure in people with elevated levels and benefit heart health.