The Flynn effect is a very complex topic, so I don’t want to get too deeply into details here, but considering the totality of evidence, it is unlikely that nut

The Flynn effect is a very complex topic, so I don’t want to get too deeply into details here, but considering the totality of evidence, it is unlikely that nutrition and living conditions have much to do with it. Here is one piece of evidence against it: for upper half of Americans (in terms of economic prosperity), the improvements in nutrition and material living condition have, to a first approximation, maxed out by 1960 at the latest. The wealthier half of Americans in 1960 had no lack of food, neither in terms of quality or quantity, and things have not got significantly better since then (if anything, you could argue that the diets today are less healthy now). Certainly, they ate much better than even the wealthiest people did back before 1700, and had much better material conditions of existence. However, the Flynn effect gains kept steadily growing decade after decade, until 2010 or so.