All this talk of portion control needs more detail. It's not just the size of the portions that the problem, it's the content. Remember that most fruit and vegetables are virtually fat and calorie free. Even meat isn't too bad as long as it's lean and not deep fried. The BIG problem is all the carbs we surround them with. All that bread, rice and pasta.
You can eat a huge portion of stir fried chicken and vegetables. Eat until you can't force anymore down. It'll still be less calories and fat than a couple of slices of pizza. And whoever stops at just a couple of slices of pizza?
Cutting out carbs is the biggest challenge for me. Mostly bread, Having a sandwich for lunch is just too convenient. Whenever I do completely stay off bread, rice and pasta for a few days I lost weight even if I do no exercise at all.