Train yourself to get in the habit of having enough, but not too much. Eat as little or as much as you need, slowly, over time, to achieve a balance that's right for you.
You learn this from a process of slowly cutting back, just a little at a time, on the foods you enjoy. If you're eating three fast food burgers every lunch, try two. If you're having two slices of pizza, have one. If you're having a piece of meat, two or three side dishes, and a couple of drinks--just have one side and one drink (and make that one water, how 'bout?)