Radio 4: The Philosopher's Arms - Sex Equality

I much prefer arguments that are based on  facts rather than 'urban myths' or extrapolations 50 years into the future. I was listening to the Philosopher's Arms on Radio 4 and heard (12min 55s in to the episode on Sex Equality) the often repeated claim that Women can run faster than Men over long distances. I think it was Beatrix Campbell talking and, in this case, the Daily Mail seems to be more accurate!

How much do I want that Snickers?

I was just mulling over one particular 'theoretical' benefit that might be gained by slow long runs. In my current case it is in the early taper stage before a marathon, but it applies to just about any time. One aspect that I thought would be interesting to guesstimate is what might the 'weight-loss' benefit to marathon improvement time be of a single run, since I don't have a 'ball-park' figure in my brain.