text: Your observation is accurate but your interpretation is a bit off.
  You don't see fat distance runners for the same reason you don't see light weight football linemen.
  The activity self selects for certain body types especially at high performance levels.
  Body builders can have low body fat and with the right training methods high MVO2 as well, but distance running is likely to result in impact injuries to their low back and legs.
  One size does not fit all.