All about the BED

Written by Dr Klaus L.E. Kaiser

Are you expecting a salacious, perhaps even a lascivious story? Sorry to disappoint you as this is not about sex but BED, an acronym that stands for “Banana Equivalent Dose” and it has nothing to do with the bananas’ prescribed curvature in Europe either (rescinded).bananas

You may wonder, what do BEDs, I mean bananas, have to do with radiation dose? Well, it’s in the nature of things, more specifically in the banana’s natural radioactivity.

Natural Radioactivity

On Earth and other heavenly bodies, solid land consists of rocks that are made up from some minerals that are made up from atoms of elements combined in silicates, carbonates, and a few other types of “-ates” and “-ides.”

There are only about one hundred of such atoms, some in several “isotopes,” that is elements or atoms of the same kind but with slightly different nuclear cores, called nuclei. The different isotopes of any element only vary in the amount of “glue” between their other (proton) parts in the nucleus. Both too little and too much of that glue makes the atoms decay at a fixed rate. Such isotopes are radioactive, meaning they naturally decompose, commonly while emitting some form of radiation.

Radioactive Radiation

Not only uranium, but even some common elements like potassium occur in nature with radioactive isotopes. The half-lives of such isotopes are in the millions of years, meaning that they decay quite slowly. For example, an isotope with a half-life of, say one million years, on average it would take one million years to reduce two of such isotopes to one.

Because of large amounts of energy contained in atoms nuclei, their decomposition is also accompanied by a large energy release. Nuclear bombs are just devices to get a whole lot of such isotope’s decay going all at once. The decomposition’s accompanying radiation is commonly measured in “rem” (Roentgen Equivalent Man) units, but the “Banana units” are easier to relate to.

The Banana Equivalent Dose

The Banana Equivalent Dose (BED) is a non-scientific radiation measurement unit but nonetheless a highly practical idea. That is most obvious in relation to the measure of radioactivity received from various foods, activities or events. As potassium salts are major constituents of all plants, eating any plant material at all will also cause you to consume some of those radioactive potassium isotopes, no doubt about it, but you ought not to worry about it. The amount of radiation from the potassium is very small and it commonly leaves your body before it is absorbed by it.

A common problem with news reports is that any numeral greater than one associated with any unit of measurement of anything under the sun tends to create unreasonable fears of such things, radiation or whatever. Let’s look into the radiation dose from the potassium isotope 40-K more closely.

Potassium Isotope 40-K

The potassium isotope 40-K has a natural abundance of only 0.01% in all the potassium compounds in the Earth’s crust and has a half-life of 1.25 billion (10^9) years. The former is a small percentage, the latter a very long time. To put it into perspective then, a human body, weighing 75 kg contains approximately 200 g of potassium in ionic form. At an abundance of 0.01% of the potassium isotope the radiation from that 40-K comes to around 5 nano-Sievert (Sievert: yet another unit of radiation measurement) or 0.000000005 Sievert over a 50-year life time.

Moreover, the 40-K isotope nuclear decay releases only beta-radiation (i.e. energetic electrons) that is not readily absorbed by soft tissue. So, even when inside the body, the radiation is most likely to exit the body before it hits another atom’s nucleus that could possibly lead to further nuclear reactions. In short, any tissue damage from that 40-K in your body is quite limited, practically negligible.

Of course it is entirely irrelevant as to where you get your 40-K isotopes from. Other fruits and vegetables that are rich in potassium, like potatoes, kidney beans and sunflower seeds will add to your consumption and exposure. Variations in soil characteristics are more important as geologically younger soils will have more of the yet un-decayed potassium isotope than older ones.

If you are still concerned on how much radiation you get from your veggies, read on.

How much Radiation?

As Stephen Petranek writes in Tomorrow in Review, “the average American gets about 620 milli-rem of radiation exposure a year from airplane flights, granite countertops, radon in tap water, working in concrete buildings, eating Brazil nuts (one Brazil nut has a BED of 2) and cosmic radiation. Your dose of radiation from the sun—cosmic radiation—escalates as you move higher than sea level—about 26 milli-rem a year in Washington, D.C., and 52 milli-rem (104 bananas) per year in Denver. That’s because 80% of the oxygen on the planet, not to mention other gases like nitrogen, is in the first 50,000 [corrected from 5,000] feet above sea level. That thin blue band around Earth that mesmerized moon-bound astronauts is really thin. In Denver, there are far fewer gas atoms in the atmosphere between you and the sun to deflect cosmic radiation. The point is that unless you want to live in a radon-free cave (unlikely you can find one) background radiation is omnipresent [and unavoidable].”


Of course, a low level of radiation exposure is not only unavoidable but is actually important for developing resistance to diseases. That fact has long been recognized in the field of hormesis or homeostasis, a sort of “natural medicine.” In simple terms, it means that a low dose of any deleterious substance will create or enhance the body’s natural defense system to cope with that disease vector. Natural background radiation, from the rocks around us, the sun and the cosmos are all part of that. However, that field of knowledge is still very much under discussion.

The rapidly increasing prevalence of some diseases, for example autism, may well be linked to a lack of benign exposure to disease vectors during childhood. Therefore, keeping your child “safe” in a near sterile environment may prevent his or her development of such natural defense mechanisms.

Before you go Bananas

So, before you go bananas over that radiation exposure from eating bananas, let me assure you, there is little to worry about. Neither your spanking-new granite kitchen countertop nor airplane travels to visit your aunt in Alaska are likely to affect your longevity one way or another. Even eating a banana or two a day will actually provide more good minerals to your body than any deleterious effect that could come from it. The Nutrition Data website claims they are good for you because of low levels of saturated fat, cholesterol and sodium and their content of dietary fiber, vitamins C and B6, potassium and manganese.

Perhaps, though, only if they are of the right curvature.


Dr. Klaus L.E. Kaiser  BioDr. Klaus L.E. Kaiser Most recent columns

Dr. Klaus L.E. Kaiser is author of CONVENIENT MYTHS, the green revolution – perceptions, politics, and facts

Dr. Kaiser can be reached