The short and pithy answer to your question is "the same way you lose fat even if you aren't fit". What this boils down to getting your food and exercise on a plan that will work for you. There's a couple ways to approach it:
- High protein diet: While some reports state you don't need more than .82g protein per lb body weight (for body builders), protein does keep you satiated longer and requires more calories to process than any other macro nutrient.
- Increase conditioning: Conditioning is anything that gets your heart rate up and improves your cardiovascular system. This includes stuff like hitting a tire with a sledgehammer, running hill sprints, barbell complexes. I find those more fun than running on a treadmill for what feels like hours on end.
- Increase work: Whether body weight work or Smolov squat programming, several people have experienced their fat trimming down even though they haven't changed their eating habits.
Chad Waterbury's article on the Pullup/Lunge/Pushup 60 day challenge sheds some more light on the last bullet point. In short, it all started out when a guy Chad was coaching said that the more pushups he does, the leaner he gets. Essentially, High Frequency Training (HFT) is very effective for body transformations. The PLP challenge is designed to maintain decent shoulder health and overall body work. The way it works is you start out with a set of 1 or 10 (depending on how many pullups you can do at once).
- Day 1: starting number of reps: pullups, reverse lunges (each leg), pushups
- Day 2: add one to the number of reps: pullups, reverse lunges, pushups
- .... keep adding one each day until
- Day 60
If you have to split the work up into sets do it. You just have to get the total number of reps in that day. You start low, and keep building. By the end of the challenge, you will be doing 60 or 69 reps on day 60 (depending on your starting point). Another important part of the challenge is not to do more than the prescribed reps.