Bananas have a small amount of radioactivity due to their high potassium content. A natural isotope of potassium called potassium-40 is radioactive. A truck loaded with bananas emits enough radiation to set off a false alert on sensors designed to detect illegal nuclear materials. However, eating bananas won’t make you radioactive—you already are!
So how many bananas would you need to eat to increase your radioactivity? The average adult has roughly 140 grams of potassium, including about 16 milligrams of potassium-40, making you 280 times more radioactive than a single banana. Consuming one banana raises your potassium-40 levels by 0.4%, detectable by a precise Geiger counter. But the effect is short-lived—your body maintains strict potassium balance, so any excess is eliminated within hours.