it is actually genetics

a lot of asians are well adapted to high starch diets, but it's not universal

especially in the smaller south-east-asian countries they don't cope with the high starch chinese diet, they need more meat

there is genes associated with tolerating high levels of starch in the diet, and they replicate in the individual's DNA, more of them, better they cope

i'm from indonesian genetics, from north Irian and i'm pretty sure my great great grandfather looked like this:

https://assets.survivalinternational.org/pictures/1234/ind-wp-dani-adg-11_940.jpg

up high in the mountains of north papua there is not very much starch around, and lots of little animals, and you might guess by looking at him that those are bones in his face