Adipose tissue retains an epigenetic memory of obesity after weight loss

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 into the future long after the athlete has stopped using the steroid. Non-professional athletes shouldn’t get too excited about using steroids, though, because the damage steroids do to the body’s own hormone systems also has lasting effects unless you plan on doing TRT for the rest of your life, which has its own downsides.

For average people this does show the importance of getting at least some exercise when you’re young. It’s much easier to get a little bit fit when you’re young which then makes it easier to stay fit in the future. Never too late too start.

I can't remember exactly what I was listening to, maybe some kind of NPR podcast.

But the doctor was mentioning that none of the influencers influencing young people to try T and Steroids (which is rampant right now) are ever mentioning that you are on a ticking clock to infertility as soon as you start this stuff. Some people can regain their fertility but it might take years, and some people are going to be permanently infertile even staying on HRT.

Plenty of those "alpha male" guys on social media are shooting blanks.