My understanding of this factoid is that it has more to do with atoms tendency to swap particles when they bump into each other. So it’s sort of through attrition all of the atomic particles in your body are swapped out over the course of about seven years. So like as oxygen and carbon dioxide, for instance, move in and out of your brain and other tissues they leave electrons and shit behind and take some with them. But it also wouldn’t be the first time I had misunderstood something.