I remember reading that during the second WW, Europeans were aghast at the appearance of Americans.
I’m pretty sure it’s a nutrition thing. Americans were/are heavier built, stronger and more developed... AND taller
There is a window of development for that stuff and if nutrition is poor during formative years... you can’t ‘catch up’ later.
One European said ‘We couldn’t believe how tall and big all of them were...’
When VietNam fell, my church adopted a SVN refugee couple with a small son and daughter. All 4 accepted Christ and learned English. Those kids became instant Americans. And how they grew and filled out. The boy became a husky 6 footer, Bible college grad teaching school. The girl blossomed into a gorgeous woman, with Hooters never ever seen on a native in Saigon. I can only credit the Lord and American groceries with how those kids turned out.
Many of those soldiers spent their 'developing years' in the Depression.