Oh I agree, I do think there are genetic factors at work as well as environmental...
I just think that is why most people may want to deny those factors exist - while providing a nice excuse for people who dont want to do the work, they also take away some hope for the rest of us.
Plus....well if the author was saying "HEY --yes--you DO have to work harder, but it can be done" that would be one thing. That would actually be a huge relief to a lot of us who have been told it IS only our lack of control that caused our problem. I would like to know it isnt entirely my fault that when I was younger and didn't know better that I didnt do better. (But now that I know better its up to me!)
I just chafe at her...hopelessness. It feels more to me like her book is saying "you are genetically screwed, your best bet is to learn to live with it and be happy".