Here's something most people don't hear before they start a GLP-1: when you eat 30-50% less food, you absorb 30-50% fewer micronutrients. Over 6-12 months, that arithmetic catches up.
The 2025 Joint Advisory from the American College of Lifestyle Medicine and the American Society for Nutrition was the first major clinical guideline to formally recommend proactive micronutrient assessment for GLP-1 patients. The advisory flagged five deficiencies as high-risk: vitamin B12, vitamin D, iron, zinc, and magnesium. Commentary in The Lancet Diabetes & Endocrinology (Prado et al., 202400272-9/abstract)) reinforced the concern, drawing parallels to nutrient depletion patterns observed after bariatric surgery.
Here's what you need to know about each of them.
Why GLP-1 Users Are at Elevated Risk
Three converging factors:
- 1.Lower food volume = lower total micronutrient intake.
- 2.Delayed gastric emptying + reduced stomach acid can impair B12 absorption specifically.
- 3.Rapid weight loss mobilizes fat-stored nutrients (vitamins A, D, E, K) unpredictably and reduces dietary fat absorption.
The pattern is well-documented after bariatric surgery, where post-operative micronutrient monitoring is standard of care. GLP-1 therapy is not surgery, but the physiology of rapid weight loss plus reduced intake is similar enough that many clinicians now apply analogous principles.
Key Takeaway: Nutrient deficiency on GLP-1s is a slow, silent side effect. You won't feel it at week 4. You'll feel it at month 6 as fatigue, hair loss, brain fog, and slow muscle recovery.
The 5 High-Risk Deficiencies
1. Vitamin B12
Why it matters: Red blood cell production, nerve function, energy metabolism, cognitive clarity.
Why GLP-1 users are at risk: B12 absorption requires stomach acid and intrinsic factor. GLP-1s slow gastric emptying and may reduce acid production. Many GLP-1 patients also take metformin, which independently depletes B12.
Symptoms of deficiency: Fatigue, brain fog, numbness or tingling in extremities, glossitis (sore tongue), mood changes.
Recommended form: Methylcobalamin (bioactive) over cyanocobalamin. 1,000-2,000 mcg daily.
Lab target: Serum B12 > 400 pg/mL; check methylmalonic acid if borderline.
2. Vitamin D
Why it matters: Calcium absorption, immune regulation, muscle function, mood.
Why GLP-1 users are at risk: Vitamin D is fat-soluble. Reduced dietary fat intake impairs absorption. Rapid weight loss releases stored vitamin D from adipose tissue unpredictably.
Symptoms of deficiency: Muscle weakness, fatigue, bone pain, low mood, poor recovery from exercise.
Recommended form: Vitamin D3 (cholecalciferol), ideally paired with K2 (MK-7). 2,000-4,000 IU daily; higher if bloodwork shows deficiency.
Lab target: Serum 25(OH)D of 40-60 ng/mL.
3. Iron
Why it matters: Oxygen transport, energy, cognitive function, hair growth.
Why GLP-1 users are at risk: Lower meat intake (especially during nausea phases) reduces heme iron. Menstruating women start at higher baseline risk.
Symptoms of deficiency: Fatigue, hair shedding, cold extremities, restless legs, difficulty concentrating, pale skin.
Recommended form: Iron bisglycinate (gentler on GI than ferrous sulfate), 18-25 mg daily. Pair with vitamin C for absorption.
Lab target: Ferritin 50-70 ng/mL (higher than many lab "normal" ranges) for hair and energy.
4. Zinc
Why it matters: Immune function, wound healing, hair follicle health, taste perception, testosterone production.
Why GLP-1 users are at risk: Reduced meat, seafood, and legume intake. Dysgeusia (altered taste) on GLP-1s may reflect declining zinc status.
Symptoms of deficiency: Hair thinning, slow wound healing, altered taste, frequent infections, brittle nails.
Recommended form: Zinc picolinate or bisglycinate, 15-30 mg daily. Always pair with 1-2 mg copper to prevent copper depletion.
Lab target: Serum zinc 70-120 mcg/dL.
5. Magnesium
Why it matters: Muscle function, sleep quality, bowel regularity, blood sugar regulation, 600+ enzymatic reactions.
Why GLP-1 users are at risk: An estimated 50% of Americans are magnesium-deficient at baseline. GLP-1 appetite suppression worsens it. Constipation is often partly a magnesium issue.
Symptoms of deficiency: Muscle cramps, poor sleep, constipation, fatigue, anxiety, headaches.
Recommended form: Magnesium glycinate for general use and sleep; citrate if constipation is the primary concern. 200-400 mg elemental daily. Avoid magnesium oxide except as a laxative (only 4% bioavailable).
Lab target: RBC magnesium (not serum — serum is insensitive) in upper half of reference range.
Nutrients Beyond the Core Five
Omega-3 fatty acids (EPA+DHA)
Reduced fish/seafood intake leaves most users below adequate intake. 1,000-2,000 mg combined EPA+DHA daily supports cardiovascular, cognitive, and skin health.
Folate
Important alongside B12 for red blood cell production. Active form: methylfolate (5-MTHF), 400-800 mcg.
Calcium
Bone health during rapid weight loss. 1,000 mg daily (ideally food + supplement combined), paired with D3 and K2.
B6 (pyridoxine)
Supports neurotransmitter synthesis and has meta-analysis-level evidence for nausea relief (Jayawardena et al., Arch Gynecol Obstet 2023). 25-50 mg daily.
Key Takeaway: The 2025 ACLM/ASN advisory's five nutrients are the priority. Everything else is supportive. Don't build a 15-pill regimen — cover the essentials well.
How to Build Your Regimen
Option A: Targeted repletion based on bloodwork. Ask your prescriber for a baseline micronutrient panel (CBC, ferritin, B12, 25(OH)D, RBC magnesium, zinc). Supplement specifically to the deficiencies identified. Retest at 3-6 months.
Option B: Proactive coverage with a GLP-1-formulated multivitamin. Covers the core five plus supporting nutrients in bioavailable forms. This is what SQ[1] Daily Essentials was built for — methylcobalamin B12, D3+K2, iron bisglycinate, zinc picolinate, and magnesium glycinate in dosages aligned with the 2025 advisory.
Most patients benefit from Option B as a floor, with Option A targeting specific gaps identified on labs.
Red Flags That Suggest Deficiency
- New-onset numbness or tingling → check B12
- Muscle cramps at night → check magnesium
- Hair shedding beyond month 3 → check ferritin and zinc
- Persistent fatigue after month 8 → check iron, B12, D
- Frequent infections or slow wound healing → check zinc and D
FAQ
Can I just take a regular multivitamin?
Most generic multivitamins use poorly absorbed forms (cyanocobalamin, magnesium oxide, zinc oxide) at doses too low for the caloric deficit GLP-1 users are in. A GLP-1-specific formula is a better fit.
Should I get bloodwork before starting supplements?
Ideally yes, but not strictly required. Baseline labs help you target. Without them, a well-formulated GLP-1 multivitamin is a reasonable floor.
When should I retest?
3-6 months after starting supplementation, then annually once stable.
Do I still need supplements if I eat well?
When calories drop 30-50%, even "eating well" leaves gaps. Supplements are insurance, not a substitute for food quality.
Is it possible to over-supplement?
Yes — particularly fat-soluble vitamins (A, D, E, K), iron, and selenium. Stay within recommended doses and work with your clinician if you're on multiple products.
This article is for educational purposes only. Talk to your healthcare provider before starting new supplements, especially if you take other medications.
These statements have not been evaluated by the Food and Drug Administration. SQ[1] products are not intended to diagnose, treat, cure, or prevent any disease.
Fill the gaps the right way. Explore SQ[1] Daily Essentials — built around the five nutrients most at risk on GLP-1 therapy.
