I'm just going to chime in here and mention that as preteens, a lot of kids with other extraordinary stressors in their lives can turn to using food as a locus of CONTROL.
That is, if you make a big deal out of it, the child learns that they have a 'handle' that they can use to leverage things from those around them. ETA: The reason why this is dangerous territory is that it's a recipe for disordered eating, which is all about control, not food.
If your doctor isn't worried about nutritional deficiencies/harm-- hearing the honest truth about what your child eats, I mean-- then it probably isn't something to turn into a battle.
This is an area where the autonomy of the child really can't help but win in the end.
Highlight what your child is MISSING as a result of the behaviors, find out if those are things that matter to either of you, and ask if s/he wants to change. Maybe explain your logic if you disagree... but... if the answer is no, then you're pretty much nowhere without that cooperation. JMO.
I'll also put a plug in, here, as someone who has a life-threatening food allergy to shellfish... it really bums me out to HAVE to forgo some social activities because I have to think about my (in)ability to be "flexible" about food. When I suggest a 'different restaurant' or opt out of sushi, I'm not being "controlling." I really don't have a choice other than "no." I'm flexible about other things-- gracious, even. But food isn't one of those things, and all too often stuff becomes ABOUT food when it doesn't even involve food directly.
So yes, being able to be flexible if there's not an organic medical reason behind it? VERY much more important than most people realize. If you refuse food (particularly as an adult), YOU OFFEND OTHERS. No avoiding it. Trust me.
