you have a really flat stomach! how do you maintain it? like sit ups or anything?

I do nothing but eat only junk and I never gain weight for some reason. And I have tried to do sit-ups to get Mirander Kerr's well toned stomach, but being the lazy ass I am, I failed. LOL. Helen, you have a really pretty face. Give me tips on how?!

Just hit me with your hotstuff.