As background, generally the way I've seen the logic about edits removing off-topic content is that it's off-topic to ask for answers about nutrition, and thus answers (or portions of answers) about nutrition are not answering the question, and removing it can't turn it into a worse answer. Of course normally off-topic tangents aren't particularly harmful, but with nutrition it's just so incredibly common for it to lead to misinformation and unproductive debates.
With that said, it seems fairly clear that historical questions like this one may indeed have nutritional answers - not necessarily in the sense of "it makes the food more healthy/nutritious!" but "people believe that it makes the food more healthy" or even "it has X effect on the nutrients in the food". That may well be one of the reasons why something is done, and answers won't be complete without mentioning it.
I would tend to then say that this case (and probably others like it) is one where we shouldn't necessarily just remove everything that mentions nutrition, especially if it's presented in a more factual manner, rather than overbroad/unverifiable "it makes it healthier" claims.
Given this, I think I'd generally be fine with things like your original answer, especially if refined/clarified to avoid the sort of overbroad claims rumtscho is concerned with. I don't think we can reasonably make/discuss those big claims, but it doesn't seem to be particularly in dispute that nixtamalization helps prevent deficiency-related diseases, or that that's one of the historical reasons for the practice.