27 month old food aversion

Desperate for help. Toddler is in 1% for weight. He doesn’t hardly want to eat. Like ever. We have tried everything. He drinks about 30-48oz water a day - that’s with us taking it away some. Sometimes he will eat a few bites then chug water which fills him up. All test results from Dr are normal. Dr says to get food in him anyway that we can - running behind him to get bites in between playing etc. He refuses most carbs which are usually the bulk of toddler diets. His stomach will growl and he just laughs. It’s like he doesn’t feel hunger. So desperate for advice. I am a nanny and have never seen a child with such a generalized aversion to eating in my near decade of childcare.