

The 7 year thing is a myth. Howtown has a very good summary on it. 7 year myth some cells are replaced but how often depends on the cell type, some never get replaced.
When you gain weight your fat cells grow, and when you lose weight they shrink. You don’t actually gain and lose fat cells the way people think. However, the stuff in those cells could very well be old. It’s a complex system and hard to sum up and I’m only friends with the biology people from college but that’s what I understand from them.
Kind of? The cells, called adipocytes, primarily store triglycerides and a few other things in a liquid form. When you lose weight that liquid gets squeezed out and used as energy, to build other chemicals your body needs, or peed straight out.
So less a shower and more getting rung out like a sponge.