Several studies have shown that most Americans are deficient in potassium. A healthy person would have to eat 700 or 800 bananas a day to get enough potassium each day from that source alone. However, too much potassium can be as dangerous as too little, as it can destroy the heart muscle. For a healthy person to reach that danger zone, he would have to eat 400 bananas a day! If someone ate too much potassium from bananas, their stomach capacity would stop them before they got sick.
In general, eating two bananas a day is a good idea for healthy people. People taking beta blockers for heart disease should be cautious, as beta blockers increase potassium levels. Diabetics may not want to eat bananas twice a day because they are considered "medium" on the glycemic index. If not, go for it! Research indicates that high potassium intake reduces your chances of dying from any physical ailment by a solid 20%.