That's one idea. The difficulty with physical effects is lack of any obvious physical effect which could plausibly affect both rich countries in mid-20th century (long past adequate nutrition phase and at slow beginnings of obesity epidemic) and poor countries in mid-20th century (still with regular starvation, and up to this day without adequate micronutrient supply in diets) at similar rates.

But then "similar rates" may very well be due to our evidence being so bad, perhaps these rates were very different, we just don't know it.