Speed

Even from casual observation, a person can see a relationship between running speed and body weight.  If you go and watch a local 5k race, you will see that the top finishers usual have low levels of body fat.  Some might attribute this to the miles and miles of training they do, but I don't.  I attribute it to their running speed.

Endurance runners often get a bad rap with their "long slow distance" training.  Images come to mind of a jogger moving painfully slow down the road doing mile after mile.  But top endurance runners do not train this slow - instead they are quite fast.  For example, in last month's Boston Marathon, Robert Cheruiyot won in a time of 2 hours, 14 minutes, 13 seconds.  This equals a pace of 5 minutes 7 second per mile.  A 5 minute mile is tremendously fast, so clearly this person is not just running long, but running very quickly.

If you look at 5k races at the professional level, the men are running just over a 4 minute per mile pace.  Again, this pace is incredibly fast and is the defining characteristic of this type of performance. 

In comparison, I have seen overweight people finish a marathon.  If running distance was the answer to weight control, then you would think that the miles put in for marathon training would be enough.  If training for and running a marathon isn't enough to control body weight, then what's next, ultramarathons?  Clearly a change in strategy is needed.

Research also shows the importance of running speed compared to distance for body composition.  In this study, the authors state that, "Relative to the effect of running distance, running velocity ... had a 4.7 times greater calculated effect on waist circumference in men." 

In conclusion, I think the evidence clearly shows that it's better to run fast than to run long for weight control.