I feel a little late coming into this thread, but here's my two cents.
For me, realizing that this was even an issue for me was half the battle. I don't know how many years I've spent being spiteful and bitter that I can't eat whatever I want like others seemingly do, and how often I've justified going overboard because, "Well she can eat a big slice of cake, why can't I?" I call that voice my inner child.
I think there's a whole chapter about this in
The Beck Diet Solution. I don't own the book (I've been meaning to buy a copy) and it's been a while since I've read it, but I'd highly recommend it. She basically explains we have to accept the fact that our bodies have their own needs different from everyone else's, and the sooner we accept that and move on, the better. And her suggested way of handling it is by saying, "Oh well."
I really want that extra helping of dessert. Oh well.
I really don't want to get up early for my walk today. Oh well.
It's an acknowledgement that we're not getting the instant gratification that we want, but that it's something we can nevertheless get through and put behind us. While easier said than done, it's something I've been working on for several months. Some days are better than others, but it's so automatic that I don't even reach the "oh well" moment most of the time.
I personally make a quick, unemotional decision, stick with it, and don't look back. The longer you debate on whether or not you should have that brownie or that extra pizza, the more tortured you're going to feel (which will only set you up for failure).
I already know what my personal limits are with how much I should eat and why, so I let that dictate the decisions I make. So when we get a box of carry-out pizza, I already know that I'm having two slices. No debating, no what-ifs, no fudging; I have my two slices (and a salad) and I'm done. SIL brings brownies home? I decide I'm having just one, no more. I have that one brownie, make sure I enjoy it thoroughly, and am not allowed to change my mind and have more after the fact. And when I'm offered a donut at a meeting, I remind myself I already had a brownie the day before and politely decline while focusing on enjoying my coffee and not drooling over everyone else's donuts in the room.
It takes a lot of time, effort, and practice. Sometimes I even got myself crying when I've had to say no to chocolate, and I've had to stop and ask myself why are certain foods so damned important that I'd let my health slide away over them? Nothing is more important than my health. I still have to stomp out my inner child every so often . . . she spent many a year getting rather spoiled . . . but with these efforts she gets quieter and quieter as time goes on.