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 actually want to know 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.
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.
BethLabQueen 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.
BethLabQueen 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: 89 → 98 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.
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Browse GL BiochemRetaRick_CA said:Blood count monitoring for micronutrients: my doctor noticed my MCV (mean corpuscular volume) trending up at month 6: 89 → 98 fL.
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 60 to 27. Supplementing.
- Vitamin D: Was already low (19 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:Vitamin D levels and micronutrients: an often-overlooked connection.
This is my experience too, for whatever a second data point is worth. Nothing to add that would improve it.