Originally Posted by
BarracksSi
Good way to put it, and that's what I've been thinking lately about low-carb eating and endurance exercising. Frankly, what we do on a bike is historically unnatural (who suspects that cavemen ran around at a high HR for five hours?), and I didn't think that a paleo-natural diet would fuel the activity well enough.
At lower heart rates and exertion levels, it's fine, but it'll have its limits.
The human body is designed to use glucose first before fat. So there is no problem with what Chaco and BarracksSi are proposing. If you are burning 750 - 1000 cals per hour, taking on some carbs is obviously not going to present a problem.
However, if you are in keytosis, and you have been there for you several weeks, your metabolism has changed to efficiently burn fat. You start with very little glucose in your muscles, but you won't bonk. Fat is a better fuel for long sustained efforts. What it is not good for would be a final all out sprint effort.
What you don't want to do is to shift your metabolism back to primarily a glucose based metabolism by ingesting too much for too long, that is, carbo loading for several days before a big ride, eating a log of goo on the ride, and indulging for several days after the effort.
From a paleo standpoint, you are telling your body "Spring is here! Sugar and starch will be plentiful. Shift back to a glucose based metabolism, and store fat for the winter." If you do that, then you have to go through the "induction" process to get your metabolism back to being fat based. That takes time.
IF you are a serious professional racer, these diets are probably not for you. If you are a regular Joe (or Fred) even at high level, it may be something to consider.