i'm very unscientific about these things. I don't know why but I didn't have any problems with cramp - may be its the slow pace? I just grabbed a handful of crsisps where available and had the salty soup. I also had a few cups of Maxim and had a couple of cups of coke at each refuelling point. apart from that I filled up the water bottle from streams at the end, but can't have had more than 400ml per section.