That's roughly what I assumed. :( Obviously, it would be nice to think that years of very unrestricted calorie intake could be "undone" by adhering to a very strict and severe calorie restricted diet later on, but that goes against intuition, and it looks like the science agrees.

I like to fast sometimes these days (my longest was a 10 day water fast) and genuinely feel like it has significant benefits, but I also realize that as I approach 40, some shit just is as it is and there's no going back and fixing it.

What a fascinating and broadly meaningful project to work on for your thesis! Maybe worth mentioning for the coincidence of it if nothing else: my sister, back in the early 00's did similar studies with rats, ageing, and nutrition for her PhD thesis. I wish I remembered the details better, but it wasn't specifically about caloric restriction. She's a tenured prof at a community college now and writes multimedia textbooks for low-cost or free distribution (because fuck the textbook industry racket). Anyway... massive respect for you delving into the science of this stuff.