A LOT.
My daily runs vary from 10k to 12k, and i never used to find it comfortable doing 5
days in a row - say, starting monday, till friday, and by friday evening i would be
so dead tired wooden and wasted, it was hardly a nice experience. Even by the 3rd
day, the "enjoyment" factor would start disappearing, and the whole thing would
start looking more and more like a chore. Those days, i was only on carbo loading,
with an occassional attempts at "calcium boosts" to help those bones. God knows if
the calcium stuff helped.
Then one day, Tom suggested trying out Gatorade, and i did exactly that. It made a
HUGE difference. It's not the tastiest thing or anything, but it works. The difference
is very clear once Im past the 3rd or 4th day of training without a rest day,
where earlier i would start drooping, now i feel, well, just Normal. The biggest
reason is it's rehydrating nature, i believe. I used to glug in litres of water
earlier - but Gatorade replaces lost Salts as well, i guess.
So far i haven't noticed any "bad" effects - except for a strange burning taste which
it leaves in the mouth, almost as if it's chemically addictive. But i don't think
that's the case. And as far as Calories are concerned, it's hardly 100 KCal per half
litre.