I don't have any good advice to share, but am watching this with interest.
My DM's attitude to food and weight has had big effects on my life (I'm now 28). When I was little, DM would tell me how lovely I was, as I was 'only skin and bone.' She'd say how grotesque it was to be fat, which I internalised to the point that I called my 2 best pals 'fat and tubby' (unprovoked) when I was 4 and, understandably, they fell out with me.
As I got older, DM would tell me she was anorexic as a teenager, because her parents put so much pressure on her to be a high achiever. I have no idea why she needed to tell me this. A few years down the line, both me and my DSis begin starving ourselves and get very thin. DM is furious and asks me if I'm only doing it because she told me she was anorexic. I turn out to be a crap anorexic anyway and turn to bulimia instead but DSis gets very thin and ill.
Fast forward to now, both of us are better but, due to anxiety/depression, both of us have ended up on antidepressants over the past few years, and have, as is often the case with ADs, gained weight. Now, I don't give that much of a fuck - I'm heavier, but at least I'm not suicidal - but sometimes I do get angry, because I feel like I'm invisible and everyone must secretly have no respect for me. DSis is off ADs and is doing well. But every time she tries to fit into an old dress, she can't and she ends up in tears. She's worried the old feelings will come back.
I'm still on ADs, which is fine with me for now, but DM is desperate for me to come off them 'and the weight will just drop off.' I never see DM eat dinner. I don't remember her ever sitting down for dinner with us during my childhood.
I love my DM to bits - she has helped me through some awful times, and I feel guilty writing this, but I want to avoid any future DD I have going through all this, and I really need to learn how to do that.