This gets cited here weekly, usually second-hand, so it is worth setting out what it does and does not establish.
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.
Where I think it is weakest: the comparator does most of the work in how this gets reported, and it is not the comparator most people think they are citing.
What I am after is which deficiencies actually show up when intake drops this far, and which are worth testing rather than supplementing blind. Not looking for reassurance. Looking for the part I have got wrong.
Figures above are from the primary publication rather than the press summary. If a number here disagrees with one you have, post yours and we will work out which of us is reading a secondary source.
Dr.SleepRoch 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.
Vitamin D levels and micronutrients: an often-overlooked connection. Obese individuals store vitamin D in adipose tissue, making it less bioavailable. As you lose fat, vitamin D can actually increase WITHOUT supplementation.
My trajectory: Baseline 18 ng/mL → Month 6 (with supplement) 42 ng/mL → Month 12 48 ng/mL. Target is 40-60 ng/mL. Adequate vitamin D supports immune function, bone health, and mood — all relevant during weight loss.
Dr.SleepRoch 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 | 75 | 23 | 55 |
| Iron | 105 | 60 | 93 |
| TIBC | 335 | 405 | 345 |
| Transferrin Sat | 31% | 15% | 26% |
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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Browse GL Biochemsarah.morrison said:Iron studies on micronutrients — important especially for women: Marker Baseline Month 6 After Supplementation Ferritin 75 23 55 Iron 105 60 93 TIBC…
Blood count monitoring for micronutrients: my doctor noticed my MCV (mean corpuscular volume) trending up at month 6: 90 → 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.
Dr.GastroMayo said:Vitamin D levels and micronutrients: an often-overlooked connection.
This is my experience too, for whatever a second data point is worth.