You would think that the best runners in the United States should know better than to fool around with diet in the days leading up to an important race. When an athlete is good enough to make a living at runing fast, it's important that they take advantage of all available resources to do so, i.e. massage, chiropractic, coaching, and DIETARY ADVICE!
Thinking he could run faster if he was lighter, it looks like Dathan Ritzenhein was trying to diet the week prior to the US National Track and Field Championships this summer. Check out this candid interview with Dathan as he descibes the last 1K. interview .
One athlete who did use all resources avalible when preparing for major competitions was Lance Armstrong. Cyclists more so than runners pay particular attention to the importance of weight, yet have figured out how to balance caloric intake and expenditure without loss of endurance and strength.
Check out this article about Lance's dietary planning posted on msnbc.com.
"To make positive adaptations to training, your body needs a slight surplus of energy. To lose weight, you need a slight energy deficit. Trying to lose significant amounts of weight while training hard can do more harm than good because it robs the body of its ability to recover, which in turn reduces the positive impact of workouts."