all of the atoms in your body are swapped out every seven years or so.

I'm not sure exactly what's true, but what you're saying seems like a factoid that gets repeated a lot but isn't really 100% true.

Structural stuff like the calcium in your bones... it would be interesting if it was really replaced on a schedule like that. It wouldn't shock me if it was getting replaced, but it would certainly be cool to learn how that would work.

Is the lens in your eye getting replaced like that? I'm trying to think of body parts that seem to not get constant automatic maintenance. How about the enamel on your teeth? Really replaced every 7 years?

Or if we're really just talking about atoms in your body, then famously the problem with heavy metal poisoning is that your body can't get rid of it. So, is it being replaced or is your body getting rid of it? Or... is it just there from before?

And if you want to get really pedantic, and I always do, what fun... Things like artificial hips or breast implants are definitely in people's bodies longer than 7 years but are not getting their atoms replaced.