Well, yeah. Adipocytes multiply when you get fat. But when you lose weight, they don't apoptose, they just shrink in volume by giving up their lipid stores.
Similar adaptions occur in muscle. The extent of new muscle fiber development (hyperplasia) is debated, so there are multiples factors influencing how muscle retains some memory of past strength ability. Once you’ve reached a level of physical strength it’s easier to return to that level in the future. This has been a topic of debate in the sports world because past anabolic steroid use could therefore carry benefits…
They’ve known this for centuries. Quoting the great Socrates:
“No man has the right to be an amateur in the matter of physical training. It is a shame for a man to grow old without seeing the beauty and strength of which his body is capable."