I don't use any tomato sauce or paste, but I have thrown 2-3 whole italian plum tomatoes in with the veggies and it works well. It's just a little bit, and they cook down, break up and almost become part of the sauce. I don't think Ive ever made pot roast exactly the same twice..always close, but since I never measure, it can vary depending on what root veggies I have, etc.