I wonder if they did eat some plants, but just didn’t get enough fiber? I eat no fiber (strict carnivore) but have no problem with regular bowel movements.

I’m curious to know what your diet is like. Eg, if you are only eating meat, do you eat more bones and sinews than the usual omnivore to get enough “roughage” for digestion?

Eg, birds at a falconry can’t be fed just the usual bird “meat”, they need to have the skin and feathers attached which is essential for their digestive tract.

They may not have understood the vegetation well enough, and stuck to meat out of caution. Apparently when they got close to the west coast they tried eating camas and got very ill the first time because they didn't prepare it properly. Lots of ways to go wrong when you are in an unfamiliar area (see also: death camas).

Why the strict carnivore diet? That is, if you don't mind me asking.

Iirc from “Undaunted Courage,” a daily diet consisted of 10 pounds of bear meat, for men who were burning thousands of extra calories a day.

I think such a diet just means you need to drink more water than your body expects. Meat digestion seems to take more water.