Energetic homeostasis and compensatory effects in humans are fascinating.. Complex systems are complex, of course, but more important here is that humans evolved during times of scarcity, with a thrifty gene. Simply exercising more or eating less doesn't evade a millon year of evolutionary pressure.

The evidence for constrained total energy expenditure in humans and other animals https://www.sciencedirect.com/science/article/abs/pii/S0960982226000643?dgcid=rss_sd_all