Common foods that are naturally radioactive include potatoes, bananas, sunflower seeds, Brazil nuts, and kidney beans, among others.  Brazil nuts are the most radioactive by far at 6600 picocuries per kg or about 1.875 BED (banana equivalent dose). The radium in Brazil nuts does not come from especially high levels of radium in the soil where the trees grow, but rather the very extensive root systems the trees develop, which cover a much larger area of the soil than most trees.

Although bananas and Brazil nuts contain very little ionizing radiation, in terms of what might actually harm a human, they are radioactive enough to trigger false alarms in some radiation sensors used to detect illegal smuggling of nuclear materials.

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