"Gorillas don't need to eat protein, because they grow their own protein in the bacteria that thrive inside of them. The gorilla consumes the vegetation to feed the bacterial colonies of their microbiome, and then absorbs the protein formed by the bacteria as they feast on the cellulose fibers of the vegetation"

https://medium.com/@westwise/how-does-a-gorilla-get-so-strong-75c68edd3c26#:~:text=Gorillas%20don't%20need%20to,cellulose%20fibers%20of%20the%20vegetation%20.

Tldr Gorillas apparently have better probiotics than we do. Also they eat so much more than us, even relative to bodymass, 18kg per day of biomass, which is equivalent to a human eating 9kg of biomass a day. I can eat a lot, but I don't think I could put away over 15+ pounds of any kind of food in a day.