You may have heard that if you can die from eating too many bananas, usually around 6-8, because you can get potassium poisoning. Here, I’ll investigate the potassium content of bananas, and see if there really is enough in them to kill you.
According to the United States Department of Agriculture (USDA), a medium banana will contain an average of 422mg of potassium. This potassium will be in a number of organic forms, but the form most abundant in a banana is potassium citrate. This is of importance, because the toxicity depends on the chemical form the potassium is found in, as well as the dosage.
To illustrate this importance, the LD50 (dosage which kills 50% of the population) of potassium citrate in a rat is 7200mg per kg body weight, whereas the LD50 for potassium chloride in most mammals is 3020mg per kg body weight.
Potassium makes up just over 38.2% of the weight of potassium citrate, so, assuming the vast majority of potassium in a banana is potassium citrate, the total amount of potassium citrate in a banana is 1105mg.
The L50 for potassium citrate in humans is unknown, but is greater than 2000mg/kg body weight (which classifies it as a very low risk chemical, meaning the exact LD50 dosage isn’t important to identify).
However, as most mammals seem to regulate potassium and other minerals in a similar fashion, for the proposes of this little investigation we can make the assumption that the LD50 of potassium citrate for humans will be similar to that of rats – 7200mg/ kg body weight (this is in keeping with the Thermo Fisher statement of the LD50 being greater than 2000mg/kg body weight).
Using the above information, we can calculate the number of bananas which will be lethal to a human. Assuming the average weight of a man is 70kg, this makes the LD50 for potassium citrate to be 7200×70 = 50400mg (or 50.4g).
This would make the LD50 for bananas to be 45.6 bananas, not 6-8 as some people claim.
This 45.6 banana estimate doesn’t take into account the digestion rate, or excretion rate for potassium (let alone the rate you can eat bananas), and so in reality is likely to be much higher. We know that the body can excrete potassium extremely efficiently and quickly when it needs to. In fact the concentration in plasma potassium levels from eating 2 bananas has been described as ‘marginal‘, suggesting that healthy kidneys are very good at filtering potassium out.
Perhaps the oral lethal dosage for potassium has been confused for the lethal IV dosage, which for dogs is 170mg/ kg body weight (according to Wiki), which is a hell of a lot lower than 7200mg. If this was the case, the LD50 would be calculated at 10.7 bananas, which is pretty close to 8.
Or perhaps there has been some mix up with the understanding of potassium, and the infamous potassium cyanide, which only takes a few hundred mg’s to kill someone… Who knows? (seriously, if you know, please comment and let me know!).
Potassium poisoning from bananas seems to be a myth, but this isn’t to say eating 6+ bananas rapidly is good to do. There is a lot of sugar in a banana, and the large amount of potassium, although not fatal, may affect the mineral balance of your plasma. For example, sodium and potassium are two closely linked minerals, and its possible that a large amount of potassium excreted may also excrete a large amount of sodium too (for better or for worse).
This Youtube video will give an overview of the information found on the article tab. If you want to know more about the topic, or want to see where the information came from, have a read of the article after you watch the video.
You would need to eat at least 45 bananas very quickly to come close to potassium poisoning – kind of impossible.