Yes. No. Bananas are slightly radioactive because they contain potassium and potassium decays.
Potassium is a necessary substance for healthy operation of your body. You would have to eat a LOT of bananas just to compete with the natural potassium dose of your body.
Other 'radioactive' potassium-rich foods include spinach, white beans, apricots, salmon, avocados, mushrooms, and yogurt.
No one ever developed radiation sickness from eating bananas.
Yes, bananas are radioactive, but so are you.
Yes, you will certainly die from radiation poisoning if you are able to eat 10,000,000 bananas at once. You may also witness chronic symptoms if you eat 274 bananas a day for seven years.
Your entire body is made of a lot cells, which are made of a lot of organic molecules, the framework of each of which is made of a lot of carbon.
A carbon atom (generally speaking) is found to possess either 12 particles in its nucleus, or 14. Atoms with 12 particles in the nucleus (called C-12) are normal and much more abundant. Those with 14 (called C-14) are radioactive and much less common, but present in some small concentration in any natural carbon sample, including your own body.
Now, in relevance to the question, banana has potassium atoms of three kinds: K-39, K-40, and K-41; 39 and 41 are not radioactive. K-40 atoms are those you are interested in.
100 grams of banana have 0.328 grams of potassium, of which 0.012 per cent is K-40. Which is to say 100 grams of banana gives you 0.00003936 grams of K-40.
Seems very small? It is. But wait.
Now, the 0.00003936 grams of K-40 that you did get has a half life of 1.25 billion years, compared to the 5,715-year half life of the C-14 inside you.
So you are much, much more radioactive than 100 grams of bananas.
Keep buying bananas!
All I know is that the oldest man alive, at 117 years old, says that one of the reasons he's lived that long is he's had a banana a day. Soooo, I'm going no.
I have been eating three to four bananas a day for the past 17 years and I am active. Radioactive would be hyperbole.