Talking to kids about eating healthy

I have really struggled with how to talk to my 12 year old about eating.  She wakes up this morning and has a bagel with cream cheese, then 1/2 a grapefruit.  Which isn't too bad, but we were headed to a brunch, where I figured there would be sweets, and she was making this pink cake for Valentine's Day.  Oh, and last night she and her friend ate a whole pint of ice cream.  I wanted to encourage her to eat something with protein before we left for the brunch.  We ended up in a discussion about refined flour and sugar and the relationship with obesity and diabetes and other chronic disease. 

I want my children to have a healthy relationship with food, but society does not support that, and neither do her friends or school environment.  And my daughter, like many 12 year old girls want to eat what her friends are eating.  I do not know how to talk to her without it sounding like, "if you eat that, you will get fat".  Which is not true.  She can eat anything and not get fat, but if she eats too much of certain things, than it is more likely that she will gain weight.