There was a paper about 10-15 years ago where they mentioned that they noticed decreased appetite and increased metabolism at higher altitudes. [1] kind of goes over this. I used to live in a high altitude town (~ 7000 ft) and definitely noticed that my appetite was much lower and whenever I traveled had much more stamina.

[1] - https://journals.physiology.org/doi/full/10.1152/japplphysio...