First off, SteveQ, if you're reading - I really did not intend to plagiarize your last blog post, I just happen to be experiencing the same symptom at the same time. I lost 6 pounds this week. Unlike SteveQ, I know why I lost them but the "why" is not germane here.
All that to say, on Monday had I run a 5 km I definitely would have broken 18 minutes 17:45-17:55 I think. Now I am 6 pounds lighter, have not run since my prediction work-out on Monday (involuntarily but not related to injury) so here I am, light, tapered and pretty much in shape (at least I was 5 days ago) so - what effect does rapid weight loss have on race performance? Tomorrow I find out.