When I used to run marathons I would discover each new season that I had a bit of a spare tire forming around the middle that just would not go away no matter how much I trained. Everywhere else was trimming nicely (and some suggested my face would look emaciated) but that little extra belly flab would not go. As an experiment one year I cut out almost all carbs for a week (meats and salads only) and the spare tire disappeared immediately. I'm not sure how healthy it is to cut out carbs during hard training and I felt weirdly exhausted during that period --but it sure made the extra belly flab go away.