How nuclear bomb testing enabled obesity research

This is the kind of thing that makes me love science. Derek Lowe has a blog entry about a letter in Nature whose authors figured out a way to determine the number and age of all the fat cells in a person’s body, and tracked that data over a number of years. The results confirm that the number of fat cells you have is set by the time you are an adult, and from then on they merely change size as you gain or lose weight. (I don’t know how this was determined previously, but I’ve heard that fact from a number of different sources.) Even if you undergo liposuction, the cells that get sucked out are replaced after a few years. There is some mechanism that keeps your population of fat cells at a pre-programmed level. They also figured out that about 8% of your fat cells get replaced every year.
So, how did these researchers determine how old a fat cell is? As it turns out, the above-ground nuclear bomb tests in the 50’s and 60’s increased the concentration of radioactive carbon-14 in the atmosphere, and the concentration has been decaying ever since to the natural background level. By measuring the amount of carbon-14 in the DNA of a cell (other parts of a cell are recycled during its lifetime, but the DNA is not) they could determine exactly when that cell was created.