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
18 support 0 contradict 0 tested null 7 mixed · 25 sources, 18 independent groups
What the evidence shows
Micronutrient deficiency is a predictable consequence of bariatric surgery, not a rare complication: iron, vitamin B12, vitamin D and calcium are the common ones, and thiamine deficiency rose from 7 to 19 percent by three months in a 41-study meta-analysis. Some is already present before surgery, so lifelong monitoring and supplementation are standard care.
The evidence (27)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| Zhu C, Liu W 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, Ingersent E, Wanberg EJ, Jegen DA, Passmore R 2025 · Endocrinology, diabetes & metabolism case reports | 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, Laurenius A, Hedberg S, Thorell A, Hägg M, Grehn S, Spetz K, Olbers T, Andersson E 2026 · Obesity surgery | 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 J, Law S, Ou C, Dong S, Huang S, Dong Z, Zhu M, Wang C 2026 · Obes Surg | observational | supports | moderate | 12-mo cohort: trace-element and vitamin deficiencies common after metabolic surgery (some pre-existing pre-op). |
| Chakhtoura MT, Nakhoul NF, Akl EA, Safadi BY, Mantzoros CS, Metzendorf MI, El-Hajj Fuleihan G 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 A, Eghbali M, Abdolmaleki F, Abbasi M, Mottaghi A 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, Sawicka A, Kędzierska K, Binda A, Jaworski P, Tarnowski W, Jankowski P 2025 · Nutrients | 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 P, Zhu X, Bardaro SJ, Mocanu V, Wills MV, Barajas-Gamboa JS, Lee Y, Corcelles R, Strong A, Navarrete S, Udomsawaengsup S, Kroh M, Dang J 2026 · Surg Obes Relat Dis | observational | supports | high | Propensity-matched cohort: vitamin D deficiency (affects 30-70%) worsens post-op bone-health outcomes. |
| Shamnad FR, Restrepo-Rodas G, Andrade LAM, Barajas-Gamboa JS, Shah N, Carretero GC, Hegazin SB, Salloum C, Chiha M, Abril C, Guerron AD, Rodriguez J, Pantoja JP 2026 · Obes Surg | observational | supports | moderate | 40% of post-bariatric patients had secondary hyperparathyroidism at 1yr, with persistent vitamin D deficiency. |
| Yanzhang L, Xiangwen Z, Hui W, Jinfeng J, Shengli S 2025 · Journal of surgical case reports | 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, Gentry S, Parretti HM 2025 · Clinical obesity | 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, Lagarteira J, Pera R, Figueiredo A, Batouxas C 2026 · Cureus | 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 Y, Ha J, Lee YH, Kim D, Lee CM, Kim JH, Park S 2022 · Obes Rev | meta-analysis | supports | high | Meta: RYGB carries higher risk of anemia and iron/B12/folate deficiency than sleeve gastrectomy. |
| Li Y, Zhang T 2025 · Diabetes, metabolic syndrome and obesity : targets and therapy | 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, Tsao LC, Chen YY, Wang BY, Yen HH 2025 · BMC Surgery | observational | mixed | low | Retrospective single-centre comparison, 21 analysed (ESG 9, SASI 12), 6 months; SASI patients received routine B12, folate, calcium and iron supplements, ESG patients none. Toward the claim: after SASI iron fell significantly at 1 month (p = 0.004) with about 25% developing transient anaemia, and zinc was 16% below baseline at 6 months (p = 0.002); after ESG calcium fell at 3 and 6 months (p = 0.027 and 0.014) but stayed in the normal range. Away from it: 'neither group exhibited any significant deficiency in vitamin B12, calcium, zinc, iron, or folate within 6 months'; iron returned to baseline, and B12 and folate rose in the supplemented SASI arm. ESG is endoscopic, not surgical; the authors say 6 months is too short to rule out long-term deficiency. |
| Spetz K, Sandsveden M, Ottosson J, Stenberg E, Aardal E, Olbers T, Andersson E 2026 · Surg Obes Relat Dis | observational | supports | high | Large Swedish registry: bariatric surgery raises long-term anemia risk; iron deficiency a key driver. |
| Xu B, Xiao T, Li J, Lu Q, Zhang Y, Wan B, Liang D 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, Sabuć A, Spalińska A, Przybyłowski J, Skibiak K, Czerwińska M, Dzedzej J, Talarek E, Gierula A, Wyszomirski K, Walędziak M, Różańska-Walędziak A 2026 · Biomedicines | 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 A, di Filippo L, Facciorusso A, Adler RA, Binkley N, Bollerslev J, Bouillon R, Casanueva FF, Cavestro GM, Chakhtoura M, Conte C, Donini LM, Ebeling PR, Fassio A, Frara S, Gagnon C, Latella G, Marcocci C, Mechanick JI, Minisola S, Rizzoli R, Santini F, Shaker JL, Sempos C, Ulivieri FM, Virtanen JK, Napoli N, Schafer AL, Bilezikian JP 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 F, Khorshidi Y, Moslehi N, Golzarand M, Asghari G 2024 · Obes Surg | meta-analysis | supports | moderate | SR in adolescents: nutrient deficiencies (iron, B12, D) frequent after bariatric surgery, requiring lifelong supplementation. |
| Guthrie T, Eccles-Smith J, Lee S, Kothari A, Pinzon Perez W, Truby H, de Jersey S 2026 · Obesity surgery | 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, Gonzaga ER, Naveed M 2026 · ACG case reports journal | 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, Mahmoud MH, Mohamed BS, Elraggal D, Elkholy MH, Abokhozima A 2025 · Obesity surgery | 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, Sami O, Sakka I, Coelho S, Dupré T, Coupaye M, Moszkowicz D, Ledoux S 2026 · Surgery for obesity and related diseases : official journal of the American Society for Bariatric Surgery | 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, Lee H, Ahn SM 2026 · Clinical nutrition research | 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, Algethami N, Almasoud A, Almuhaimeed S, Alshahrani A 2026 · International journal of surgery case reports | 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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