Anonymous wrote:OP here. I appreciate the constructive comments posted. A few more bits of info:
Weight gain due to overeating - my son sees it and she admits to it. She started gaining some last year but most came over the summer. Due to their schedules, they only saw each other once since school got out.
They have known each other and been friends for 5 years. First real relationship for both. It is typical HS dating - officially together, casual, yet independent.
I couldn't care a lick about how much she weighs. I only care about helping a son who has come to me for advice and about avoiding a lingering body issue for her as she gets older.
In a perfect world, this is a learning experience and positive growth experience for both - and a situation where they either continue their relationship or preserve the friendship.
OP, I think you need to think about what you can actually influence here. I don't think you should tell your son he should "help his girlfriend avoid a lingering body issue." It's too much pressure for him, and it's not his responsibility. (Heaven forbid she one day commits suicide due to depression and your son feels he is somehow guilty!) He's not responsible for what she feels. Give her some credit.
However, what you CAN influence, as a PP pointed out, is your son's development. Your son should focus on being a good, thoughtful and honest person. This definitely includes not allowing his friends to discuss his girlfriend's body. He should defend her and walk away if it doesn't stop. He should also be honest with his girlfriend if he can't get over her weight issues. It's HIS shortcoming, not hers. It's better than him staying with her and constantly judging. She deserves better.
He could also take the long view and love her for who she is. (a lot of us were 20 pounds lighter in our 30s than in our teens.)