Collecting this in one place because it comes up every few weeks and the answer is always assembled from scratch. It is about micronutrient cover, and it is deliberately narrow — everything I am not confident about is marked as such.
What is actually established
A sustained drop to 1,100 or 1,200 calories reliably under-delivers a predictable set: B12, vitamin D, iron, folate, zinc and magnesium. Two of those are worth testing rather than guessing because the tests are cheap and the symptoms overlap with everything else — ferritin and B12. The rest a decent multivitamin covers, and there is no benefit in megadosing any of them.
The condition it depends on
The caveat that iron should be tested before supplementing, not after. Supplementing iron into normal stores is unpleasant at best and harmful in haemochromatosis.
The practical version
Cheap and worth having: ferritin, B12, vitamin D. Everything else on the deficiency list is adequately covered by a standard multivitamin at ordinary doses.
What I am not sure about
The question I want answered is which deficiencies actually show up when intake drops this far, and which are worth testing rather than supplementing blind. Happy to be told the question itself is wrong.
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.
Blood count monitoring for micronutrients: my doctor noticed my MCV (mean corpuscular volume) trending up at month 6: 91 → 97 fL. This flagged potential B12 or folate deficiency.
Sure enough, B12 had dropped from 620 to 340 pg/mL. Started B12 injections monthly and MCV normalized within 2 months. GLP-1 agonists can impair B12 absorption — this is a real clinical concern that deserves routine monitoring.
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:
| Marker | Baseline | Month 6 | After Supplementation |
|---|---|---|---|
| Ferritin | 70 | 18 | 55 |
| Iron | 100 | 60 | 88 |
| TIBC | 320 | 390 | 340 |
| Transferrin Sat | 30% | 15% | 29% |
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.
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View ResultsDr.ReproEndo said:Iron studies on micronutrients — important especially for women: Marker Baseline Month 6 After Supplementation Ferritin 70 18 55 Iron 100 60 88 TIBC…
Vitamin and mineral labs to check while on micronutrients — my doctor orders these quarterly:
- B12: Can drop due to reduced GI absorption. Mine went from 650 to 380 — now supplementing.
- Iron/Ferritin: Reduced food intake = reduced iron. Ferritin dropped from 71 to 28. Supplementing.
- Vitamin D: Was already low (22 ng/mL), now taking 5000 IU daily.
- Folate: Stable, no issues.
- Zinc: Slightly low, added a multivitamin with zinc.
Nutritional deficiencies are a real risk when you're eating significantly less. Don't skip your labs!
NeuroNate said:Blood count monitoring for micronutrients: my doctor noticed my MCV (mean corpuscular volume) trending up at month 6: 91 → 97 fL.
Second this. The detail I would add is minor and it is already implied above.