> During adulthood, the fat cells themselves just get larger.
While true, it's also important to note that the lifetime of a fat cell is around ten years. Maintaining a decent diet for around ten years (no mean feat!) should be sufficient to leave you bereft of the actual adipose cells.
I also wonder how this intersects with transgender stuff — there's a reason why HRT is referred to as "second puberty", as it resets and changes a lot of underlying biological mechanisms and produces a lot of interesting epigenetic effects (While it does boil down to "replacing the sex hormone", both estrogen and testosterone have major effects on the body's immune system, etc. — actually this is one of the reasons I suspect that there's such a high comorbidity of autoimmune diseases within transgender people pre-HRT — their immune system is all out of wack! Mine calmed down a lot after starting and a year in I no longer get seasonal allergies). There's a huge lack of data in this regard though because transgender bodies are generally not felt to be worth studying outside of "health risks", even though there's a huge amount of information we could glean about how everyone's* body functions from it. Personally, I wonder whether second-puberty "resets" what the body decides is the baseline for fat storage.
* — and for anyone in doubt, we have around 90 years of HRT now that shows it's essentially completely safe (outside of the mid-80s when the estrogen being given was synthetic and non-bio-identical, and outside of the health risks of various things for trans women changing to be roughly equivalent of cis women's health risks).