Comment by nonameiguess

It won't matter for your level of performance. A hike isn't a race. I'm assuming you don't care about finishing the hike faster and simply being out in the wilderness at all is the main point, the longer the better as long as you still get home by the time you have something else you need to do there.

Aside from that, this isn't a well-understood topic. Even extremely lean humans have more than enough fat to fuel crossing North American without technically neeeding to eat anything. Fat is less efficient to mobilize than glycogen, and glycogen is less efficient than free glucose already in the bloodstream, so there's some tiny bit of gain there possibly, but frankly, as fast as these guys are going, they're still far enough below lactate threshold that the energy efficiency gain is unlikely to be any real contributor to a faster finishing time. Beyond that, you can't deplete glycogen just from running a marathon, unless you were already depleted at the start of the race. You definitely can and will in longer races, but not a marathon.

Instead, what I'm pretty sure is happening here is you're just hacking the way fatigue works. Your body has more than enough fuel to do insane amounts of work without eating, but bodily systems for doing work are regulated by predictive models. There is no literal fuel gauge in your brain or muscles. They're guessing how much you have left and those guesses are conservative because selective pressures of all animals in the past pretty strongly leaned into leaving something in reserve just in case. If you suddenly find yourself in a struggle to the death, you need to be able to give it your absolute all, and that will require mostly if not entirely glycogen, which means your body's natural regulatory systems will work very hard to keep you from depleting it, so even if you have plenty left, if it's going quickly, you'll get more tired and sore than it was being depleted less quickly. Your autonomic systems don't know you're going to stop at 26.2 miles and eat a giant feast 20 minutes later and the chance of a tiger randomly popping up on the course is effectively 0. All it sees is you're depleting energy stores far more quickly than you can replenish them over the long term and it tries very hard to keep you from doing that.

In a sense, this is all endurance sport really is, training away and hacking away your body's inhibitory mechanisms to get as close as you possibly can to expressing your true physiological limits, but nobody will ever truly get there.