There are 422 milligrams of potassium in a medium-sized banana. The amount of potassium recommended for adults is 4,700 milligrams per day; therefore, an average banana provides 13 percent of the daily recommended amount.
In addition to being good sources of potassium, bananas contain Vitamins C and B6, magnesium, manganese and fiber. One medium banana provides about 110 calories and is naturally free of fat, cholesterol and sodium.
Potassium is an essential nutrient that plays a key role in muscle development and strength, heart health and nerve function. A deficiency in potassium can lead to dizziness, heart palpitations and muscle cramps. Besides bananas, other potassium-rich foods include spinach, sweet potatoes, avocados and yogurt.