I wasn't particularly overweight beforehand...I was 5' 10" 145 with 9 to 10% body fat. I recently dropped 10 pounds over the past 2 months and noticed a HUGE difference in my running. Some people say you only get 2 seconds per mile, but I got about 3 second per mile. So, same course, same heart rate with the garmin, my easy run went from a 6:30 to a 6 flat. Also, much easier recovery from long runs and strenuous workouts. I highly recommend losing weight if you're debating it. It really does help. I just cut about 600 calories a day and/or did a little extra mileage.