Nova/BM training/weight loss

[RacersEdge]

I caught most of this show a couple times the past few days. It's about a group of fairly regular people training for the Boston Marathon. Interesting stuff - especially how your heart and cardio system become more efficient as you train - een with the possibility that your heart can actually grow during training.

But while their cardio was improvong greatly as they went from running more miles over this year or 2 (?) traing program, almost NONE of them lost weight - and there was definintely some fat to lose there. The doctor made the comment that "diet is the best way to lose the initial weight while exercise is crucial to maintaining the loss".

So is eating 300 calories a day less better than expending an extra 300 calories a day in terms of weight loss? I thought it was basic arithmetic on calories consumed versus calories spent, but this doctor said different. Comments?