Metabolic & Cardiometabolic
bariatric surgery causes micronutrient deficiencies (iron, B12, D, calcium)
In plain terms: Does bariatric surgery cause micronutrient deficiencies?
Strong support Metabolic & Cardiometabolic
Part of: 🩺 bariatric / metabolic surgery
RefutedContestedStrong support
consensus score 0.74
Yes—iron, B12, vitamin D, calcium and related deficiencies (and anemia/secondary hyperparathyroidism) are common post-op, malabsorptive procedures worse, supplementation mandatory.
📅 Last reviewed: 2026-07-15 ⓘ
Evidence ladder
How far up the ladder this claim has climbed. A high consensus on a low rung means "consistent so far," not "proven in people."
Top evidence so far: All trials, pooled (Meta-analysis)
MechanismIn-vitroAnimalObservationalRCTMeta-analysis
How the studies fall
20 support 0 contradict 0 tested null 7 mixed · 27 sources, 20 independent groups
The evidence (27)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| Zhu 2026 · Ann Med | meta-analysis | mixed | high | Meta-analysis found serum zinc declined after bariatric procedures, supporting need for postoperative monitoring and supplementation. |
| Donigan EC et al 2025 · study_type: observational | n-of-1 | mixed | low | Case report: 39-year-old on semaglutide following prior bariatric revision surgery developed severe lumbosacral polyradiculopathy from thiamine and vitamin E deficiency, improving with supplementation. |
| Lundgren E et al 2026 · study_type: RCT | observational | supports | low | Substudy (n=285) of the BEST randomized trial comparing sleeve gastrectomy vs RYGB one year post-surgery; both groups showed diet-and-supplement micronutrient intake below recommended levels for multiple nutrients, with only minor differenc |
| Yang 2026 · Obes Surg | observational | supports | moderate | 12-mo cohort: trace-element and vitamin deficiencies common after metabolic surgery (some pre-existing pre-op). |
| Chakhtoura 2024 · Cochrane Database Syst Rev | meta-analysis | mixed | moderate | Cochrane SR: vitamin D deficiency common post-op but evidence on optimal oral dose to correct it is low-certainty. |
| Karimi Behnagh 2024 · Obes Surg | meta-analysis | supports | moderate | Meta-analysis of 41 studies found thiamine deficiency rose to 19% at 3 months post-surgery from a 7% baseline before declining by one year. |
| Humięcka M et al 2025 · study_type: observational | observational | supports | moderate | 10-year prospective cohort of 155 bariatric patients (sleeve or gastric bypass); prevalence of iron (9.0%→18.7%), folic acid (1.3%→11.6%), and B12 (7.1%→17.4%) deficiencies significantly increased over follow-up (p<0.05 to p<0.001). |
| Kachornvitaya 2026 · Surg Obes Relat Dis | observational | supports | high | Propensity-matched cohort: vitamin D deficiency (affects 30-70%) worsens post-op bone-health outcomes. |
| Shamnad 2026 · Obes Surg | observational | supports | moderate | 40% of post-bariatric patients had secondary hyperparathyroidism at 1yr, with persistent vitamin D deficiency. |
| Yanzhang L et al 2025 · study_type: observational | n-of-1 | supports | low | 9-year case report of a post-RYGB patient with severe deficiencies in vitamin D, calcium, iron and other nutrients accompanying chronic Guillain-Barre-like neurological deterioration. |
| Haughton S et al 2025 · study_type: meta-analysis | observational | supports | low | Rapid systematic review of 83 case reports (74 studies) of vitamin/micronutrient deficiencies presenting >2 years post-bariatric surgery (mostly RYGB, then BPD); most frequent were vitamin A (n=15), copper (n=14), vitamin D (n=23), some lea |
| Remelhe Sá S et al 2026 · study_type: observational | observational | supports | low | Case report: 23-year-old woman 2 months post-RYGB developed thiamine deficiency (20 ng/mL) and folic acid deficiency (1.7 ng/mL) causing sixth cranial nerve palsy, resolved with supplementation. |
| Kwon 2022 · Obes Rev | meta-analysis | supports | high | Meta: RYGB carries higher risk of anemia and iron/B12/folate deficiency than sleeve gastrectomy. |
| Li Y et al 2025 · study_type: observational | observational | supports | low | Narrative review of perioperative nutritional management in metabolic/bariatric surgery stating that postoperative micronutrient deficiency risk is significantly increased, requiring dietary and supplement management. |
| Wu TL et al 2025 · study_type: observational | observational | mixed | low | Retrospective comparison (n=21) of ESG vs SASI; both groups showed transient iron declines at 1 month (recovering by 6 months) and calcium/zinc declines in ESG/SASI respectively; no B12 or folate deficiencies observed with supplementation. |
| Spetz 2026 · Surg Obes Relat Dis | observational | supports | high | Large Swedish registry: bariatric surgery raises long-term anemia risk; iron deficiency a key driver. |
| Xu 2025 · Obes Surg | meta-analysis | supports | moderate | Meta-analysis of 43 studies found copper deficiency prevalence of 16-28% across years post-MBS, highest after biliopancreatic diversion. |
| Dębski J et al 2026 · study_type: observational | observational | mixed | low | 80 adults pre/post metabolic bariatric surgery (6 months); iron deficiency/iron-deficiency anemia occurred only in non-Mediterranean-diet-adherent group (10.4% vs 0%), confirming postoperative iron deficiency risk. |
| Giustina 2023 · Rev Endocr Metab Disord | meta-analysis | supports | moderate | Expert recommendations: vitamin D deficiency highly prevalent before and after surgery; routine supplementation/monitoring required. |
| Zolfaghari 2024 · Obes Surg | meta-analysis | supports | moderate | SR in adolescents: nutrient deficiencies (iron, B12, D) frequent after bariatric surgery, requiring lifelong supplementation. |
| Guthrie T et al 2026 · study_type: observational | observational | supports | moderate | Prospective cohort of 69 pregnant women post-bariatric surgery; 81% developed a micronutrient deficiency during pregnancy, most commonly iron (72%) and B12 (54%), followed by vitamin A (30%) and vitamin D (30%). |
| Madej J et al 2026 · study_type: observational | n-of-1 | supports | low | Case report: post-RYGB patient developed profound micronutrient deficiencies and acute liver injury after starting semaglutide, requiring ICU care and reversal surgery, illustrating compounded nutritional vulnerability from altered GI anato |
| El-Masry H et al 2025 · study_type: meta-analysis | meta-analysis | supports | moderate | Systematic review/meta-analysis (PRISMA, 14 studies, 1049 patients) of nutritional outcomes after revisional bariatric surgery post-sleeve-gastrectomy; found notable rates of vitamin D, B12, albumin, calcium, zinc, and iron deficiencies acr |
| Chappard H et al 2026 · study_type: observational | observational | mixed | moderate | Prospective cohort (n=313) post-RYGB/sleeve-gastrectomy given personalized biology-based supplementation; mean number of deficits remained stable (~3.5) through 3 years, with hyperparathyroidism more frequent after RYGB (23% vs 9%) but anem |
| Yoon Y et al 2026 · study_type: observational | n-of-1 | supports | low | Case report of 13-year-old post-sleeve-gastrectomy; developed vitamin D deficiency post-operatively despite otherwise normal biochemistry, with suboptimal supplement adherence. |
| Alhomaidi YA et al 2026 · study_type: observational | n-of-1 | mixed | low | Case report of a 43-year-old post-sleeve-gastrectomy patient who developed supraphysiological B12 (1300 pg/mL) from over-supplementation, resolving after cessation; discussion notes RYGB commonly causes B12 deficiency while sleeve patients |
| d10-17116-endoskop20263203112 2026 · Endoscopic Surgery | observational | supports | moderate | Retrospective study of 103 patients 1-3 years after one-anastomosis gastric bypass; vitamin D deficiency in 46.6%, iron deficiency in 41.7%, B12 deficiency in 35.0%, calcium deficiency in 33% post-surgery. |
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