I believe that your body will make you eat enough food to keep you at the weight you are. For example, today I've eaten less than I usually eat. Now for the rest of the day I feel like I need to eat. When I eat that extra food I am satisfied because I now have eaten enough to maintain my current weight. If I did not eat the extra meal I would feel that I didn't eat enough. I'll want more food but if I can resist and do this routine again for the next several days or a week, I will have reset my inner food meter to eat just enough to maintain my new weight. It doesn't matter if you are thin or obese your body is set to maintain your current weight and you must willingly and consciously eat more or less food to reset this automatic system..
I believe what begins to happen is that your stomach feels like it has shrunk and after several days, less food fills you just as before when a larger amount of food filled you. I think it's more important to eat smaller portions than it is to eat large portions of low fat and low cal foods. Eventually you will eat regular foods and you'll still feel the need to eat large portions. Drop the amount of food and you will get used to smaller portions and you will lose weight.
When you gain weight it's because you eat past the level of feeling full and eat till you are uncomfortably stuffed. This is a dangerous thing to do because you are again beginning to reset your system. photo credit: USDAgov via photopin cc