Dear Heather,
I don't really know the answer to this, but I have encountered the idea of extra weight equating with self- protection too.
If that is the case, perhaps it means that unconsciously there is an intense fear within us of having our survival critically threatened? That would make biological sense, as fat is nature's way of preparing for harsh conditions, such as being abandoned by a parent, perhaps. So maybe somehow the extra weight comes from a deep fear of abandonment by our caregiver? Why those fears would extend into adulthood, I don't know though. But so much of our emotional makeup is residual, so it could make sense.
I was a skinny child too, but I started to get noticeably chubbier when I was 15 years old. That was when my mother started her affairs, and would leave the family for 6-9 months at a time (we never expected her to come back each time she did it, so the pain was enormous).
When I was 17, my mother was home again and I started dieting and became extremely thin. But I gained back all the weight (and more) when I left home to live in another city (abandonment issues again, no doubt). I became completely addicted to food when I was 19, when I started working in the country as a horse groom, for an extreme NPD sufferer. She was 100 times worse than my mother! By the end of that year I was bulimic and very thin again.
However I think the way people react to intense fear of abandonment does not always result in gaining weight, and being chubby is not necessarily a sign of emotional illness either. Two of my sisters became much thinner and one could barely eat at all, for example. (Kind of like what Janet described) . I attribute this to genes, as those two sisters were born to another mother. When my sisters put on a bit of extra weight, its usually a GOOD sign for them, and comes when they are feeling secure and happy.
My youngest sister was the most enmeshed child with our mother of all of us, and she has become progressively fatter over the years and is now noticeable obese. My mother is a huge part of her life and has financially supported her and her various husbands for her entire adulthood. My parents bought her a succession of franchise businesses (worth over 100K each), and their home. I really think my sister's obesity is tied in with the enmeshment with our mother somehow.
My weight now is something like 20 pounds more than I prefer (aesthetically speaking), but I have held onto it for these past 4 years because I am working through the disproportional sense of shame I feel about having a little extra weight. Its been an extremely strengthening experience, in terms of feeling loved by my partner, and getting about in the world as a real person rather than as a `hot chick'.
As my shame has begun to dissolve (and it has!!), I am feeling myself becoming more energetic and gravitating towards physical activities that I enjoy. For example, I am walking for 1 1/2 hours a day now through a quite hilly area (to take my photos of wild-life), and it feels so different to when I would go to the gym, and the utter fear that would drive me. I think the fear of Fat is was a toxic feeling for me, also inherited from my mother.
Thanks so much for this thread Heather; it has been so good writing about this and reading everyone else's experiences.
X Bella