So is height, and historically there have been large differences in height between the rich and poor. In modern developed countries, however, there doesn't seem to be any significant difference based on socioeconomic level. That leads me to believe that these "nutritional deficiencies" don't exist and are not what is causing any observed gap in IQ or academic achievement.

Do Asian Americans have better nutrition than other categories?

Correlated, yes. Highly correlated - I doubt it. Einstein didn't get that way by eating enough blueberries and salmon oil or whatever.

Now of course, if you are raised on a diet of sugar and lead-laced air and water, you won't reach your natural genetic potential. And if you are raised by billionaires with a live-in chef and nutritionist and tutors, in a place with squeaky-clean air and water, you might reach your full potential.

But those things merely optimize, or impede, the raw material you were born with.