Go with multiple smaller meals a day---talking 5-6 meals, versus the traditional 3 squaure meals Mom used to make. Make sure your getting enough complex carbs and protien; Try and stay away from simple sugars and processed foods.
Think: Chicken, steak, fish, any fruits or vegtables, pasta, rice. Thses should be your staples.
Don't get too sucked into the "High protien low carb deal". Essentially, it works, because it forces people to pick healther foods----lean meats and veggies. But you still need your carbs or you'll gas out if your serious about being a martial artist.
Whey protien.....if your pressed for time, and can afford it, buy it. I use it all the time, especially post workout. It's a great time-saver, and a quick source of protien. But don't think you need it, by any means.