evidence: A theory has been doing the rounds for years that suggests too many bananas can kill you. [...] Catherine Collins, a dietician at Kings College London told BBC recently that to ingest enough potassium to kill you, you’d have to eat around 400 bananas at once. [...] In short, you cannot eat a fatal dose of bananas – unless (there’s always an exception to every rule) you are suffering renal failure and are on dialysis, in which case a strict low-potassium diet is necessary to prevent potassium build-up.