I've historically been a big skeptic of the CKD/carb-loading theory, but I've been revising my opinion somewhat over the last few months. I've been on low-carb the entire time I've been a serious exerciser, so you'd think if anyone's body was trained to run on ketones, it'd be mine. However, I've periodically had some trouble with carb-bonking and overtraining, and I do have much better workouts when I'm eating higher maintenance carb levels than if I'm in a fat-loss phase and trying to keep it under 50g. I don't routinely go off-plan and eat sugar/flour -- I have a real dessert every couple of months, and that's about it -- but I've noticed that when I do, I can count on having a *great* workout the next day. For example, I ate a (large, frosting-loaded, sick-makingly sugary) piece of wedding cake last week, and effortlessly cranked out an extra mile during the next day's run. Other times, I've been able to increase my weights by 10 or 20 lbs over the previous session, which isn't small potatoes either. I *can* certainly get through my workout pattern on relatively low levels of carbs, but I don't think I could make major performance gains in lifting or in running without bumping them fairly high or doing some kind of CKD strategy.

I'm not endorsing a CKD/carb load/refeed/whatever for the vast majority of people, but I do think there's some usefulness to be found there if you are a SERIOUS exerciser (marathon runner, body-builder, power-lifter, etc.).