The Committed Effective Dose Equivalent for K-40 is 5.02*10^-9 Sv/Bq or 1.86*10^-2 rem per microcurie ingested. (For the uninitiated, recall that 1 Sv = 100 rem.)
Recall from my previous post that a banana contains about 10.92 Bq of radioactive K-40.
Run the numbers, and you find that the CEDE from eating one single banana is about 0.005 millirem.
These numbers can vary all over the shop, depending what your source is for the Potassium concentration, and the banana mass, but one thing is clear.
Living within 50 miles of a nuclear power plant in the US exposes you to an average dose of 0.09 millirem per annum, or 1.64 Banana Units.
Annual dose from living within 50 miles of a coal fired power plant: 0.03 millirem, or 5.45 Banana Units.
This “Banana Dose” is perhaps very useful in attempting to explain infinitesmal doses to members of the public.
(Interestingly, some of the anti-nuclear people just HATE this supposedly deceptive concept.)