The body prioritizes survival over lean tissue gain when presented with extra calories due to historical starvation risks.

“but the body is not just going to go oh yeah we got some extra calories let's just lay down some lean tissue it doesn't make sense because from the body's perspective the number one thing it's trying to do is keep you alive long enough to reproduce and then once you've done that it's just trying to um prevent you from starving like the the risk of dying from starvation over the course of human history is way is magnitudes greater than like diseases from too much nutrition I mean that's basically a 20th 21st century problem”