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Micronutrient deficiency risk on GLP-1 — anyone have experience?

emma_london Tue, Sep 2, 2025 at 1:21 AM 10 replies 1,226 viewsPage 1 of 2

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emma_london

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Sep 2, 2025 at 1:21 AM#1

This is the version of the explanation I wish somebody had given me, written down before I forget what confused me. 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

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. Tell me what I have not thought of.

— emma_london · corrections welcome and will be edited into this post with credit

26 21sarah_nash92, FitDadDave, RunnerRach and 23 others

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julia.endo

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Sep 2, 2025 at 2:30 AM#2

emma_london 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 → 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.

Last edited: Sep 2, 2025 at 8:30 AM

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JessicaH_TX

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Houston, TX

Sep 2, 2025 at 3:39 AM#3

emma_london 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 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 74 to 31. Supplementing.
Vitamin D: Was already low (25 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!

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newstart_MO

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Springfield, MO

Sep 2, 2025 at 4:48 AM#4

JessicaH_TX said:
Vitamin and mineral labs to check while on micronutrients — my doctor orders these quarterly: B12: Can drop due to reduced GI absorption.

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.

Last edited: Sep 2, 2025 at 10:48 AM

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