Hi there Alex, well taking up yoga would make you more flexible in the way of stretching in similar ways to your martial arts stretching so there is no real need for you to take up yoga. I dont think your diet will have any effect in stretching, unless you have lots of excess fat on your legs that is preventing your legs from getting closer to other parts of your body (Ive seen it~).
I suggest that you stretch dynamically, there is a wealth of info on this on the forum here. This is the fastest way to achieve functional flexibility for MAists.
Cut me Mick!