Well, I was just trying to make a point about the official guidelines and standard treatment protocols and how basically none of it reflects the findings from those papers I found while I was researching for my own purpose. I wasn't extrapolating from my experience to the rest of us, but my own experience helps me understand what I find in those papers and vice versa. Specifically for zinc, I suggested anybody could test that with a BG/ketone meter cuz of the effect of zinc on BG/insulin, with ketones being a proxy for insulin level. I mentioned zinc because of the effect I read in those papers. BG and insulin are primary factors for the topic of this thread. Indeed, some of the papers I read look at the correlation between zinc and diabetes type 2, either as preventive or curative. If I understand correctly, preventive doesn't seem to work, but curative seems to work to some degree due to the effect on BG/insulin/HOMA-IR. The implication here is that whatever causes diabetes type 2 also causes zinc deficiency, if not in parallel, at least down the line.

To answer your question, how would I know if I had a deficiency. I can't be sure if all I know is what effect I get from supps, if I don't look at internal status with blood work for example. But it's simple logic. The premise is there's homeostasis of everything, and this requires adequate intake and internal status. (Above this adequate level, excess is stored or excreted, but this doesn't serve our purpose here. We're dealing with toxic effects of excess at this point.) Lack of adequate intake and status suggests supplementation will likely have an effect. Therefore if there is an effect, then it's likely there was a deficiency. However, the logic doesn't necessarily go in reverse, i.e. if there is a deficiency, then supplementation will have an effect. That's because if there's multiple deficiencies, and we only supplement with one, we're left with other deficiencies that could prevent the supps from having its effect. It's the water barrel analogy. This is one reason why many supps come combined with other supps, like vitD+calcium, CalMag, or plain old multi-vit, etc. So you can see why I can't be sure there is or was a deficiency, but you can also see it's a reasonable way to see possible deficiencies.

In my journal, you can read about the vitamin A protocol I did recently. I saw a tremendous effect on specific symptoms. Here too, I can't be sure, but the effect was so strong and obvious and immediate and up to now persistent, there's very little doubt in my mind.