Generally, I keep my carbohydrates low, less than 100 grams a day if I can. I do a fair amount of running and strength training. I participate in regional amateur competitions for the same.
I'll be doing a multi-week backpacking trip, involving roughly ~15 miles a day of trail hiking. Lots of altitude gain/loss, and carrying a ~40 pound pack. In the backpacking and hiking world, protein is treated as a nice-to-have second class citizen, and carbohydrates are much lauded for their easy energy. Everything is noodles, rice, flour, and other pulverized carbs.
Anecdotally I "know" that distance runners need a lot of carbs and I'd imagine that ~6 hours a day of strenuous backpacking is in the same ballpark. Specifically though my question is:
Are there established guidelines for when a fitness activity requires significant carbohydrates in the diet beyond what can be provided via ketosis?
I don't mind eating carbs for two weeks if necessary, but I'd like to understand why they're necessary beyond just the folk wisdom of "because you need carbs for energy". I would imagine Inuit people weren't lounging about all day and managed without the carbs.
Re-asking this a slightly different way, how does someone know that they need to have carbohydrates in their diet in order to maintain a given level of aerobic activity?