One of the tips the great Jeff Galloway purports in his article is to avoid caffeine and lists it as a diuretic. Recent research passed on by Dr. Mirkin points to caffeine being an aid in training rather than a hindrance. Caffeine blocks pain receptors and allows one to go longer than normal and does not act as a diuretic during intense exercise. This was proven in a study that Dr. Mirkin mentions in one of his articles that he passed on in his e-zine. Personal anecdotal evidence comes in the form of 7 attempts at 100 miles on the bike completed last year during the Summer in the intense heat of the Southwest US. Exercising beyond my capabilities often causes my back to ache. Over the course of these attempts I found that taking in caffeine either in the form of an iced coffee or diet coke every thirty miles or so allowed me to to work at levels higher than normal. Eventually I was able to complete the distance in 5:46 minutes. No it's not a pro-time done in less than 5 hours, but it is less than 6 and acceptable.