At a Loss (for words)

This actually may be too personal to share here. But for lack of a better, more appropriate venue (ie a private therapist) I'm just going to let it all hang out.

I had the strangest conversation tonight with my mother.

A quick detail: I've always been heavy, to various degrees. My mother has always been trim. Different body types, metabolisms, and reactions to food.

I'm a thirtysomething woman who hasn't lived at home for a looooooong time, has a decent career and a very loving, appreciative long-term boyfriend.

So, on to the bizarre fiasco that was tonight's conversation with my mother.

It started with me relating how I'd just had dinner the night before with an old friend from high school and how it was a shock -- a SHOCK -- to see how much he had aged. He looked so old. I, rather vainly, was babbling about how I couldn't believe how well I looked in comparison.

My mother (speaking genuinely): "Well, you're beautiful. You've always been beautiful. That's just how you are."

Me (acknowledging privately that every parent thinks their child is perfect): "Well, thanks Mom, that's nice. I don't know about being beautiful and all that, but I am just saying that I certainly don't think I look as frazzled as [my high school friend] does."

Mom: "No, you've always been beautiful, and I'm not jealous. I'm not jealous. I never have been.

Me (confused): "Well, why would you be jealous? I look just like you (although bigger, of course).

Mom (out of the *effing* blue): And I've been doing a lot of research, and reading, and BMI..it's' nothing we can control, I mean body mass, or index, it just is what it is, and society says things, but that's not what we should believe about ourselves, and it's just not something we have a choice over.

Me (rendered speechless): ?????????????????????

OK, that's the conversation to the best of my recollection. I'm befuddled. How did we get to my BMI from a very innocent and fairly vapid discussion about how I am determined to believe I am somehow immune from all signs of aging?

I realize this could be some heavy mother/daughter stuff, so sorry to lay it all all out there. I just wanted to put it in writing before the details get blurred and I forget. It may be relevant tomorrow when I wake up feeling like an 18-wheeler ran over me.