To top it off, that logic is fundamentally lacking. Your parents can easily be carrying genes for things which are not expressed in them, but which do express in you. (See for example, blue eyed kids of brown eyed parents - if each parent had a parent with blue eyes, it's perfectly possible to get a blue eyed kid even though neither parent is expressing the blue eyes themselves.)

I mean, if you're going to go for the 'genetic excuse' argument, at least understand the basics of how genetics work! The doctor would've had to get a heck of a lot more family history than just mom and dad.

If it helps, I think one of the reasons why I pick up on stuff so quickly is that I live with my parents and they both buy into the diet = health thing. So I get into arguments about it with them all the time, keeps me on my toes. :)