Andy, I can only go by the common calculators like this one.
http://www.healthstatus.com/perl/reload.pl I haven't done any research into how valid they are.
My calculation was based on a person weighing 160lbs who would use 94cal in 15 min walking at 4mph. I'm sure that we will all differ but the calculator suggests that .running at 5mph (ie 12 min mile) would use 154. I know if I run regularly I need to eat more (and take less insulin) and don't put on weight. If I stop running then I can really only eat about 1500-1600 cal a day without putting on weight .(the joys of being an 'older' woman)