don't pay attention to the posters telling you to lose weight. That's the last thing a runner should try, not the first. Run a lot, do workouts, make sure your easy days are easy, average at least a race a month and enjoy yourself. When (and if) you get down to 13:45 for 5000m and are desperate for that last 2 or 3% improvement, then come on here and we'll discuss your optimal running weight.