Why does this report matter, and how did Nutriessential prepare it?
Bariatric surgery is one of the most effective long-term treatments for severe obesity. It produces two major clinical benefits: sustained weight loss and improvement in obesity-related comorbidities.
Research studies have documented the benefits of bariatric surgery but have also raised concerns about nutritional abnormalities resulting from altered gastrointestinal anatomy, reduced nutrient intake, and impaired absorption of essential micronutrients. Lifelong monitoring and appropriate supplementation are essential components of post-bariatric care, according to a study.
Several studies have demonstrated that patients undergoing bariatric surgery remain at significant risk of long-term micronutrient deficiencies that may occur both before and after surgery. The management of these nutritional abnormalities requires close monitoring and adjustment based on individual needs.
After gastric bypass, malabsorption, dumping syndrome, kidney stones, altered intestinal bile acid availability, bowel obstruction, ulcers, gastroesophageal reflux, and bacterial overgrowth negatively affect nutritional status in some patients.
Other risk factors for poor nutritional status include:
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Reduced dietary quality
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Inadequate dietary intake
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Altered nutrient absorption
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Poor adherence to nutrient supplementation
With careful management, health-care professionals can assist with long-term weight-loss success and minimise the risk of acute and long-term nutritional complications after bariatric surgery.
Given these concerns, the Nutriessential research team conducted a comprehensive review of published clinical studies to evaluate the prevalence, causes, and management of micronutrient deficiencies after bariatric surgery.
We aim to highlight the importance of long-term nutritional surveillance, patient education, and targeted supplementation strategies following bariatric surgery.
There are many studies using short-term data on nutritional deficiencies, but our report also includes studies documenting the long-term prevalence of micronutrient deficiencies. This report highlights evidence on vitamin deficiencies that occur several years after bariatric surgery.
What happens in bariatric surgeries?
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Sleeve gastrectomy, commonly performed, involves resection of the stomach to create a tubular “sleeve” along the lesser curvature.
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One-anastomosis gastric bypass (creation of a gastric pouch and a single gastrojejunal anastomosis) and Roux-en-Y gastric bypass (formation of a gastric pouch, a gastrojejunal anastomosis with a 100–150 cm alimentary limb, and a jejunojejunal anastomosis with a 75 cm biliopancreatic limb ) are the malabsorptive procedures that reduce nutrient absorption by bypassing gastrointestinal tract segments.
These anatomical alterations lead to both macro- and micronutrient deficiencies and complicate long-term health maintenance.
Are bariatric surgeries effective, and how are they associated with nutrient deficiencies?
According to a 2025 meta-analysis that included studies with over 10 years of follow-up, the excess weight loss (EWL) after sleeve gastrectomy (SG) and gastric bypass (GB) procedures was 58.3% and 56.7%, respectively.
The SLEEVEPASS trial demonstrated more favourable outcomes for GB than for SG (43.5% vs 50.7% EWL). In the Swedish Obese Subjects (SOS) study, 10 years after surgery, remission of hypercholesterolemia, type 2 diabetes, and hypertension was observed in 21%, 36%, and 19% of patients, respectively
In sleeve gastrectomy, resection of the gastric fundus reduces the production of intrinsic factor and hydrochloric acid, which further impairs the absorption of iron and vitamin B12. Folic acid deficiency is associated with caloric restriction.
In Roux-en-Y gastric bypass, the stomach is reduced to a small pouch, and food is diverted to the distal jejunum via a gastrojejunal anastomosis, thereby reducing caloric intake.
In one-anastomosis gastric bypass, constructing a shorter biliopancreatic limb lowers the risk of nutritional deficiencies.
The Report
Report from study 1:
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A study using electronic medical records identified nutritional abnormalities, weight loss, supplement adherence, and gastrointestinal symptoms among patients undergoing bariatric surgery. Among 231 patients, the majority were women (78.8%) undergoing sleeve gastrectomy. Average preoperative BMI and weight loss more than 2 years after surgery were 43.4 ± 7.1 kg/m2 and 33.5 ± 12.4 kg. The most common pre- and postoperative abnormalities are shown in the image below.
Adherence to multivitamins declined from 90% to 77% at ≥2 years. Initially, gastrointestinal symptoms were predominant. 6.5% of patients had thiamine deficiency.
Report from study 2:
This is a meta-analysis of 54 articles on the long-term prevalence of vitamin deficiencies lasting more than 5-17 years after bariatric surgery. The most prevalent vitamin deficiencies after surgery were vitamin D, E, A, and K. A subgroup analysis revealed an increasing prevalence of vitamin A and folate deficiencies over time.
Roux-en-Y gastric bypass was associated with a higher rate of vitamin B12 deficiency. Studies conducted in Europe had a higher vitamin A deficiency (25.8%) than in America (0.8%).
Report from study 3:
A decade after bariatric surgery, there was a significant increase in the prevalence of iron, folate, and vitamin B12 deficiencies. The prevalence of vitamin D deficiency decreased. Differences in iron metabolism parameters were noted between patients who underwent sleeve gastrectomy and those who underwent gastric bypass surgery.
Gastric bypass surgery was independently associated with an increased risk of iron and vitamin B12 deficiency.
What does the report conclude?
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Despite achieving durable weight loss, nutritional abnormalities remain challenging after bariatric surgery.
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Adherence to nutrient supplements is an important consideration in addressing the problem.
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Targeted vitamin supplement programs are recommended due to variation across study regions, surgical procedures, and follow-up periods.
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Regular consultation and blood investigations with a healthcare provider are necessary after bariatric surgery.
References
Zarshenas N, Tapsell LC, Batterham M, Neale EP, Talbot ML. Investigating the prevalence of nutritional abnormalities in patients prior to and following bariatric surgery. Nutrition & Dietetics. 2022;79(5):590-601. doi:10.1111/1747-0080.12747
Chen, L., Chen, Y., Yu, X. et al. Long-term prevalence of vitamin deficiencies after bariatric surgery: a meta-analysis. Langenbecks Arch Surg 409, 226 (2024). (Source)
Humięcka M, Sawicka A, Kędzierska K, Binda A, Jaworski P, Tarnowski W, Jankowski P. Prevalence of Nutrient Deficiencies Following Bariatric Surgery-Long-Term, Prospective Observation. Nutrients. 2025 Aug 10;17(16):2599. doi: 10.3390/nu17162599. PMID: 40871627; PMCID: PMC12388966.
