Can you die from eating too many bananas? --- Yeng, Minneapolis, Minn.
Marshall Brain Answers:
Let's start with the basics. According to the Food and Agriculture Organization of the United Nations (FAO), "Banana and plantain do not contain significant levels of any toxic principles." So it is not like there are any toxic surprises in bananas (unlike, say, the cassava plant, listed on the same page, which contains cyanide).
Therefore, the place that people might get the idea that bananas could be toxic probably comes from the potassium that bananas contain. Despite the fact that potassium is an essential mineral, potassium can be toxic in large doses. It is so toxic, in fact, that potassium chloride is one of the substances used to kill people by lethal injection. Too much potassium in the bloodstream causes problems with the nervous system and eventually cardiac arrest if the dose is high enough. An overdose of potassium like this is called Hyperkalemia
So the question then becomes, would it be possible to eat enough bananas to cause potassium poisoning? Since the U.S. RDA for potassium is 4,000 mg or so, and since one banana contains about 400 mg, you would have to eat 10 bananas just to hit the RDA. Obviously that is not toxic - that's the recommendation.
So to get a toxic dose of potassium from bananas, you would have to eat far more than 10 bananas.
If you look up the lethal dose for potassium chloride on a page like this, the oral value is 2,600 mg per kilogram. If you weigh 75 kilograms (165 pounds), you would need to consume 75 * 2,600 = 195,000 mg of potassium to reach fatal levels. That's 487 bananas worth. Potassium chloride is only about half potassium, so you might need to eat fewer bananas (containing K rather than KCl) than that to achieve toxicity, say by half. But the result is the same - It is hard to imagine that people who are healthy are going to be killing themselves with bananas. It's hard to imagine someone eating 25 bananas in a day, much less 250.
The one thing that might change the equation would be a situation where the banana-eater's body is not processing potassium properly. For example, people with kidney failure who are on dialysis are told to avoid bananas because of the potassium. This dialysis page says, "The mineral potassium is found in many foods, especially fruits and vegetables. Potassium affects how steadily your heart beats, so eating foods with too much of it can be very dangerous to your heart. To control potassium levels in your blood, avoid foods like oranges, bananas, tomatoes, potatoes, and dried fruits." The kidney is the organ that normally regulates potassium in the bloodstream, so once the kidneys fail there can be a problem.
Some medicines (e.g. Diovan for blood pressure) change the way that potassium is processed, and might also lower the number of bananas needed to reach toxicity.
[[[For hundreds more questions and answers, CLICK HERE]]]