Gorillas Don't Eat Meat

Back in the day, Ken Norton Sr. tried a vegetarian diet. He was in superior condition, strong and ripped to shreds, taking on guys like Ali, Frazier, and Foreman. He noticed a difference and went back to meat.

Then there was this guy
https://www.elitereaders.com/man-climbed-mt-everest-alone-goran-kropp/
What the article didn't mention is that he was eating freeze-dried food and became emaciated. It took weeks of rest and lots of yak milk/meat to bring him back. He had planned to canoe the Atlantic before he died.

I believe you need tons of animal fat and protein when under heavy physical stress.