As serious runner it is recommend striving for an ideal weight. How the less weight how more rapidly you are at the finish.
A reduction of a pounds body weight can make a difference at 6.2 miles (10 km) running contest for 15 up to 20 seconds.
A method to stipulate the ideal weight is by means of a calculation where the weight, length and udder scope are involved. See: Calculation ideal weight.
Because this method gives not always the correct picture, you can better look to the fat percentage. See for this: Calculation fat percentage.