Hi NickyJ- I just want to say I agree with what everyone else has said 100%. I think you can see that we all pretty much feel the or have felt what you are feeling, but for different reasons, but yes the basic reason is our self esteem.
One of the OP's mentioned her relationship with her diet obsessed mum. My mum was the same, but more with exercise. Even now, as an adult the first thing she says to me when she sees me relates to my weight/appearance. I think I used sabotage a lot too. It's like I'm her trophy when I look good. There is more to us than what we look like. We have a brain. I grew up with being teased, and called names. So it took a long time when someone found me attractive, or complimented me, to believe them.
But, the sabotage thing, I find can hit when perhaps we have lost some weight, and start to see improvement. You are around the 1/2 way mark, and it's an easy place to feel comfortable with where you are size wise - afterall, look what you've lost so far! But then the head stuff is still there. And that starts to come to the fore again. All the old feelings. You may question if you deserve this. I don't, but I know I don't care about myself enough. Negative self talk can be such a part of our life that it happens automatically, and we don't realize we are doing it. It affects how we feel about everything. I've been doing pretty good this time round, but yesterday, I swear, I was tempted to have a taste of things I shouldn't. It was real temptation. So, even though I haven't felt like that so much this time, it still happens - to all of us. I've been reading a good book, DR Phil. It's to do with how to cope with the 7 worst days of our life. He really focuses on how we choose react to something. We can't avoid life's trials, but we can choose how to react. Sometimes we need help with that. This is what I got out of it and I thought it might help you and others: To choose how to react, we really have to be aware of how we ARE reacting. (My words not his). Try to listen to the thoughts that are going on in your head, and if they aren't helping you, change them. You have to be your own best friend.
We don't put down our best friend, we build them up.
Here's some more hugs. You're not alone.