They do, but it does not take much for economic pressure to make one seemingly small change with wide ramifications e.g. a plant or two which are not economically viable, get substituted, and turn out to be critical, then leading to chronic deficiencies (iirc the British navy got scurvy back after they switched from lemons to cheaper limes, or maybe between two kinds of limes and one had significantly lower levels of vit c).

It could also be interactions between the cultural diets and new products historically unavailable to that culture, which are either improperly processed (maize caused a lot of pellagra in europe) or has problematic interactions with components of the cultural diet (I don’t have an example for that, but grapefruit is famous for its medical interactions so nutritional interactions don’t seem impossible).

I don’t think it should be the first thread of investigation but it certainly should not be dismissed out of hand if nothing else bears fruit. That is how you get scurvy.

> but not if we are just suddenly seeing it now

FTA: “Fischer and her collaborators combed through the medical records of patients who had received emergency dialysis between 2012 and 2015 at any Harris Health hospital. Out of the 346 cases of kidney failure in uninsured or undocumented patients, 17 percent had no readily identifiable cause. That percentage was staggering to the researchers. It suggested that thousands of emergency-dialysis visits in Texas annually may be attributable to CKDu“

⇒ it seems (part of) the reason we suddenly started seeing this is that we recently started looking for it.