Distance running is supposed to burn your muscles for quick glycogen, leaving you with smaller and smaller muscles over time and eventually reducing your capacity to do much of anything else.
I've also read that constant running elevates cortisol to the point of convincing your body it needs to store a lot of extra fat. This would be evolutionarily useful because if weird crap is going on in the world and you're running a long way to survive, the extra bit of blubber will do you well when you get to your new home and have to figure out what to eat. Good for Grok once or twice in a lifetime, bad for Korg to be doing consistently.
But you've just got to wonder why the Tarahumara have such amazing legs. From the legends I've read and the endurance they maintain, they ought to look like floppy sheets of skin on wooden planks. For reference, here's a picture of a dumb white guy showing poor foot form alongside a real runner who knows how to use his feet.
Maybe it's the corn beer?
Steak, eggs, potatoes - fruits, nuts, berries and forage. Coconut milk and potent herbs and spices. Tea instead of coffee now and teeny amounts of kelp daily. Let's see how this does! Not really had dairy much, and gut seems better for it.