I just finished round 1 of modified FOLFIRINOX (appointment Monday, then infusion pump until Wednesday). Based on my experience, I would absolutely not fast or withhold fluids before, during or after chemo. (Bearing in mind, of course, that lack of appetite and gastro upsets of all sorts can throw that plan out.) I am still trying to catch up on fluid and food four days later, and I can tell I'm undernourished and underwatered. We even talked this afternoon about pushing fluid the day before chemo. I was told to do that during an earlier, unrelated chemo course to prevent kidney damage, but I think it may help with this as well.