Many everyday foods are naturally radioactive, including bananas, Brazil nuts, potatoes, shellfish, and lima beans. The radioactivity comes from elements these foods absorb from soil and water, primarily potassium-40 and radium. At normal dietary levels, none of these foods deliver enough radiation to harm you, but the range of radioactivity across different foods is surprisingly wide.
Why Foods Contain Radiation at All
Radioactive elements exist naturally in soil, water, and the atmosphere. Plants pull these elements up through their roots alongside the nutrients they need to grow, and animals accumulate them by eating those plants or filtering water. The most common radioactive element in food is potassium-40, a naturally occurring form of potassium that makes up a tiny fraction of all the potassium on Earth. Since potassium is essential for life, every living thing contains some potassium-40. It’s been part of biology for billions of years.
Other radioactive elements show up in specific foods. Radium concentrates in Brazil nuts. A form of polonium accumulates in seafood. These aren’t contaminants from nuclear accidents or pollution. They’re part of the natural background radiation that has always existed on Earth.
Bananas: The Famous Example
Bananas are the go-to example of a radioactive food because they’re rich in potassium, and about 0.01% of all potassium is the radioactive isotope potassium-40. Eating one banana delivers roughly 0.1 microsieverts of radiation. Scientists and science communicators sometimes use the “banana equivalent dose” as an informal way to put tiny radiation exposures into perspective.
That said, eating more bananas doesn’t actually increase your radiation dose. Your body tightly regulates its potassium levels. When you eat extra potassium, your kidneys simply flush out the excess. The total amount of potassium-40 in your body stays essentially constant regardless of how many bananas you eat. This makes the banana equivalent dose a useful illustration but a slightly misleading one: you can’t accumulate radiation by bingeing on potassium-rich foods.
Brazil Nuts: The Most Radioactive Common Food
Brazil nuts contain far more radioactivity than bananas, and for a different reason. The trees that produce them (native to the Amazon basin) have exceptionally deep root systems that pull radium from the soil and concentrate it in the nuts. Measured levels of radium-226 range from 17 to 27 millibecquerels per gram, with radium-228 slightly higher at 18 to 31 millibecquerels per gram. That’s roughly 1,000 times more radium than you’d find in most other foods.
Interestingly, Brazil nuts grown in different regions of South America show similar radium levels. This suggests the concentration is driven by the tree’s biology, actively bioaccumulating radium, rather than by unusually radioactive soil in any particular area. The tree itself is the concentrator. Even so, eating a few Brazil nuts poses no measurable health risk. You’d need to eat enormous quantities over long periods to approach any concerning dose.
Potatoes, Lima Beans, and Other Everyday Foods
Potassium-40 is the main source of internal radiation from food, and it shows up in a long list of common items: white potatoes, carrots, red meat, lima beans, and leafy greens. Essentially, any food high in potassium is also measurably radioactive. The same potassium your doctor might encourage you to eat for heart health carries a trace of potassium-40 along with it.
Root vegetables like potatoes and carrots are particularly notable because they grow in direct contact with soil, giving them more opportunity to absorb naturally occurring radioactive elements. Lima beans and other legumes are potassium-dense, putting them higher on the list as well. But again, your body’s potassium regulation means eating more of these foods doesn’t change your internal radiation level in any meaningful way.
Seafood and Polonium-210
Shellfish and certain fish accumulate a different radioactive element: polonium-210, which dissolves in seawater and concentrates as it moves up the food chain. Shrimp show some of the highest levels among commonly eaten seafood, with polonium-210 activity measured at around 12.3 becquerels per kilogram. Eel runs similarly high at about 12.6 becquerels per kilogram. Fish with lower levels, like sea bream, come in under 1 becquerel per kilogram.
Polonium-210 accounts for more than 85% of the radiation dose people receive from eating seafood. The total annual dose from seafood consumption ranges from roughly 83 to 255 microsieverts depending on age and how much seafood a person eats. For context, the average person receives about 2,400 microsieverts per year from all natural background sources combined (cosmic rays, radon in air, food, and water). Seafood’s contribution is a small slice of that total.
Low-Sodium Salt Substitutes
One food product with surprisingly high radioactivity is low-sodium salt. These products replace some or all of the sodium chloride in regular table salt with potassium chloride, which means they contain far more potassium-40. Researchers measuring salt products found that low-sodium substitutes had potassium-40 activity as high as 45,936 becquerels per kilogram. Regular iodized table salt, by comparison, measured as low as 66 becquerels per kilogram. That’s a roughly 700-fold difference.
This doesn’t mean low-sodium salt is dangerous. The amounts people use in cooking are small, and the radiation dose from seasoning your food is negligible. But it’s a striking example of how potassium content directly tracks with measurable radioactivity in a product many people keep on their kitchen counter.
How Much Radiation You Get From Food
On average, food and drinking water together deliver about 0.29 millisieverts (290 microsieverts) of radiation per year, with a typical range of 0.2 to 1 millisievert depending on diet and geography. That represents roughly 12% of the average person’s total annual background radiation of 2.4 millisieverts.
Your body has handled this level of internal radiation for as long as humans have existed. Potassium-40 has been present in living organisms for about 3.5 billion years, and was actually seven times more concentrated in the early stages of life on Earth than it is now. Cells evolved with radioactive potassium as a constant companion, and the body’s potassium channels carefully regulate how much stays inside cells and how much gets excreted. Eating a diet rich in potassium-containing foods simply doesn’t change your body’s radioactive potassium load, because excess potassium is filtered out within hours.
The practical takeaway is simple: all food is slightly radioactive, some foods more than others, and none of it is a health concern at normal dietary amounts. The radioactivity in a Brazil nut or a banana is real and measurable, but it’s a fraction of the background radiation you absorb just by existing on a planet made of radioactive rock and bathed in cosmic rays.