Meta-analysisindependent cross-checkabstract checked I-BAR-121 standard review
Trials comparing bypass and sleeve: vitamin and iron deficiency
Comparative risk of anemia and related micronutrient deficiencies after Roux-en-Y gastric bypass and sleeve gastrectomy in patients with obesity: An updated meta-analysis of randomized controlled trials.
Overview
Kwon et al.. Obes Rev 2022 · PMID 35048495 · DOI 10.1111/obr.13419
Anaemia and iron deficiency were similar after bypass and sleeve, but B12 deficiency was about twice as common after bypass.
Does the study support the specific claim? Partly · Methodological quality: high
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Compare deficiencies RYGB vs SG
- How was the study done?
Meta-analysis of RCTs
- How many people, animals or samples were studied?
10 RCTs
- What was actually found?
B12 deficiency higher after RYGB
- How large was the observed effect?
RR 1.86
- What do the results mean in everyday life?
Type of operation matters
- What are the study's limitations?
Few trials
- What does it say about Elawady's specific claim?
Refines the claim
- Do the results apply to Germany and Europe?
Applicable
- What can explicitly not be concluded from this study?
Very long-term rates
Scientific in-depth review
1. Full reference
- Authors
- Kwon et al.
- Journal
- Obes Rev
- Year
- 2022
- Identifier
- PMID 35048495 DOI 10.1111/obr.13419
- Verification
- verified – PubMed efetch 2026-10-26 + Crossref API
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
not stated in abstract
2. Research question
Do anaemia and related micronutrient deficiencies differ after RYGB vs sleeve gastrectomy?
3. Study design and population
- Study design
- Meta-analysis – Systematic review and meta-analysis of randomised controlled trials
- Population
Patients with obesity randomised to RYGB or SG
- Country
Multinational
- Period
not stated in abstract
- Sample size
10 RCTs
- Inclusion and exclusion criteria
RCTs comparing RYGB and SG reporting anaemia or iron/B12/folate deficiency
4. Methods and endpoints
- Exposure / intervention
RYGB
- Comparator
SG
- Endpoints
Anaemia, iron, B12, folate deficiency
- Statistical methods
Relative risks; GRADE
5. Actual results
- Results
No significant difference in anaemia (moderate certainty), iron deficiency (high) or folate deficiency (moderate). B12 deficiency higher after RYGB: RR 1.86 (1.15-3.02) (high certainty).
- Absolute risks
not reported in abstract
- Authors' conclusion
RYGB requires more stringent B12 supplementation and surveillance than SG.
6. Strengths
- RCT-only
- GRADE
7. Weaknesses
- Few trials, deficiency definitions vary
8. Risk of bias
- Orienting tool
- AMSTAR 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- low
- Rationale
RCT meta-analysis with GRADE.
9. Assessment of the statistical interpretation
RR 1.86 CI log-symmetric approximately.
10. Relevance to the specific claim
Shows deficiencies are procedure-dependent (B12 mainly after bypass).
11. Independent contrary findings
12. Transferability to Germany and Europe
International RCTs.
13. Overall methodological judgement
High-quality comparative evidence.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | low |
| Precision of results | moderate |
| Directness | direct |
| Reproducibility | replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Long-term differences.
15. Linked fact checks
- Bariatric surgery causes lifelong deficiencies of iron, B12, vitamin D, calcium and protein, requiring lifelong supplements. – Studies with mixed or unclear results
- Gastric bypass is preferable to sleeve gastrectomy (less reflux) and can fully treat type 2 diabetes; for patients who fail dieting, bypass rather than sleeve should be chosen (2021 statement). – Studies contradicting or limiting the claim