You need to eat plenty of good foods right now, not try and diet down if thats what youre getting at. Just clean up your eating habits, eat clean, and get stronger. You can get as lean as you want but until you build some more muscle and strength youre not going to be very fast regardless. Starting track in itself will increase your caloric expenditure a lot, couple that with cleaning up your diet and eating foods that are beneficial to you as an athlete and cutting out the ones that arent, you will get leaner very quickly.
