I & a buddy of mine have always debated on how much concern a runner should have for dietary control, I think there should be a consistent focus on restricting certain foods (high acidity, high sugar, high fat) while he believes that as long as you aren't eating a meat lover's pizza an hour before your race, you shouldn't worry too much about what type of fuel so much as how much.
For reference, we are both high school xc/tf athletes, and both have an efficient metabolism (mine is probably higher)