I second what LMS said. I get the frustration when they refuse all the time. It's tedious, it's hard work, it's all consuming, day in, day out.
I hate seeing DS especially when he's next to kids younger than him (more than a year sometimes) who weigh more than him. But other than a speech 'delay' he's healthy, meeting all milestones but is just tiny (2 at the end of the month and still not even 10kgs and well under all percentile lines.
But long story short, he's still gaining weight albeit very slowly and health professionals aren't concerned so I need to heed their advice or I'd be a mental case at each 'meal' time.
Please have a read through this site, it has been a godsend to me http://ellynsatterinstitute.org/htf/iwfr1.php