Let's face it, most of like to eat. Many of us like to eat a lot. And "carbo-loading" before a race seems like a really, really good excuse to do exactly that - pig out, guilt-free. But is it?
I have to say I've tried it a few times and it hasn't really worked. I've mostly done it in (short, amateur!) stage races or before a big road race. My performance didn't improve - seemingly, because how could I really tell? I didn't endure any better and I spent more time on the loo both pre and post race. But I did it in the '80s and the science has moved on, presumably.
The theory's good, though. In my day (the '80s, like I said) a few days to a week beforehand I'd ride to exhaustion a few days in a row - and I do mean exhaustion - whilst cutting back the carbs. And then I'd 'over-recover' for a few more days by backing off the miles, resting, and ingesting more than enough carbs than strictly necessary to simply refuel. Anecdotally this is still a popular idea - you 'fly' a few days after riding yourself into the ground. Somehow - this is the dodgy bit in my opinion - the body not only takes on what it needs it adds a bit more as a gluttony bonus, as though it senses you are about to do something extreme, or maybe even stoopid. But how does it know (insert something plausible about stimulating glycogen synthase here)?
And why would we evolve such a curious turbo-boost function? It doesn't seem likely, really, does it? If you over-eat you should simply egest or store (as fat) what you don't have room to conserve. Why would there be a secret hidey-hole for extra carbs?
Of course it's possible that waves of feast and famine coupled with our ancient mania for endurance walking have set this up for us. It's possible.
So much for the good old days. These days sports scientists generally believe it does work, even if it's just via the placebo effect (and who cares, as long as it works?). And they have generally ditched the ride-to-exhaustion bit. Rather you just do the diet and rest bit. (Which sounds a bit too convenient for me, but anyway...). The theory remains that training less ('tapering') but eating more carbs (ie eating more low-fat sugar and starch but slightly less protein and even less fibre) over 1-4 days will measurably boost your available muscle glycogen levels before an event. So it does work, indeed it just sounds like resting and recovery to me - and it's even easier than ever. But remember it's still not a licence to pig out!