>>2118793I do those about 3-4 times a week and i eat efficiently enough to be fit af and keep going. I have a book about competitive orienteering which talks pretty well about this subject, i'm not going to translate all that technical rant to english, but TL;DR it says your energy is produced as follows (pic related):
>bpm 50-70%, this is the zone you can keep up with the whole day.Predominantly from fats.
>bpm 70-80%, this is the zone that will wear you up in a couple of hours.Evenly from fats and carbs.
>bpm 80-90%, this is the zone you can keep up with from ten minutes to a hour.Predominantly from carbs.
>bpm 90-100%, this is the maximum stress your body can take, you last just some minutes and closer to 100% even seconds.Carbs and immediate PCr- and ATP reserves from your muscles.
Also somebody of those bushcraft youtubers did a rather good video from more outdoors-specified point of view where he talked also about packing weight and stuff like that, but i can't remember who it was. If someone knows what i'm talking about pls link.