B12Beth said:

A sustained drop to 1,100 or 1,200 calories reliably under-delivers a predictable set: B12, vitamin D, iron, folate, zinc and magnesium.

Iron studies on micronutrients — important especially for women:

My ferritin cratered at month 6 from reduced dietary intake. Iron bisglycinate 36mg with vitamin C brought it back up. Don't wait for anemia symptoms — test proactively.

A narrower follow-up, since the general answer is now clear:

What would you measure differently if you were starting again?

DoseLogDan said:

Iron studies on micronutrients — important especially for women: Marker Baseline Month 6 After Supplementation Ferritin 66 19 56 Iron 96 61 79 TIBC…

There is a second half to this that has not been said yet. The mechanism and the magnitude are separate questions. Agreeing that something happens says nothing about whether it happens enough to act on.

Happy to go further on any of that.

Closing the loop on my own question.

Late follow-up. I did not do what was suggested, I did something adjacent, and it worked; posting the difference in case it matters to somebody.

traveltech_sara said:

The mechanism and the magnitude are separate questions.

Right, and the exception is worth naming rather than left implied, because the exception is where people get into trouble.