Posted: 24/11/2014 at 15:05
A 10 stone man (different for ladies) running seven minute miles burns 100 calories per mile. If he runs 14 minute miles, he burns 50 calories per mile.
A 20 stone man running seven minute miles burns 200 calories per mile.
So, work it out from there.
There is of course the after burn of running that lasts for a while and results in a raised metabolism and burns off calories.
3500 calories is about a pound of fat.
So if a 10 stone man runs a marathon in 3 hours, he burns 2600 calories and not enough to lose a pound of fat (yes I know other stuff burns first).
So the OP just eats too much.