From what I've read in several arctic diaries, people didn't try eating lichen until they were starving in winter when the cariboo were emaciated or had left the area and there was absolutely nothing else to eat. On return trips they went back to frozen carcasses to scavenge parts they'd left behind. They may have popped an adrenal gland and found it made them feel better. They broke bones and made a broth (if they had some vegetation or seal oil to make a fire with) and threw in other stuff they had on hand, like leather. In areas with no vegetation, just seals, after couple of weeks they'd get so bored that they'd try eating all sorts of things to get a different taste or texture - to me that is one reason to have vegetables to break up meat boredom.

Eliminating grains & dairy made it clear what they had been doing to me, but it was a complete elimination diet that really put my body in tune with what individual foods did to me. Even the difference between grass-fed meat and grain-fed meat feels different. My brain always feels sharper on grass-fed meat and wild fish.