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Risks & Possible Complications

Weight Loss Surgery (Bariatric)
What the published evidence says about risk

This page summarizes the risks of weight loss surgery in plain language, using figures reported in large published studies. This is general information, not your individual risk assessment — Dr. Irshad will review your own risk factors with you directly as part of your consent discussion before surgery. Figures below are for the two most common procedures, sleeve gastrectomy and gastric bypass (Roux-en-Y); your surgeon will discuss which is being recommended for you and why.

Risks & possible complications

  • Death within 30 days — very low, roughly 1 in 500 to 1 in 1,250 (0.08–0.2%), based on large multi-center registries and randomized trial data.
  • Any complication — roughly 10% in large real-world registries, though can be higher (13–21%) in closely-monitored clinical trial data that captures more minor events; gastric bypass tends to run somewhat higher than sleeve gastrectomy.
  • Leak at a staple or connection line — roughly 1 in 600 (about 0.17%) for sleeve gastrectomy, somewhat higher for gastric bypass.
  • Bleeding — roughly 0.5–1.8%, and has been decreasing over time with modern stapling techniques.
  • Blood clots (deep vein thrombosis / pulmonary embolism) — roughly 0.3%.
  • Return to the operating room within 30 days — uncommon, well under 5%.
  • Long-term: a vitamin or mineral deficiency (particularly iron and vitamin B12) develops in a substantial proportion of patients over years, despite taking recommended supplements — regular blood work and lifelong supplementation are part of follow-up care.
  • Need for a second (revision) operation over 5–10 years — roughly 3% (sleeve) to 1.5% (bypass) by 5 years, rising further with longer follow-up (up to roughly 12% by 10 years in some registries).
Your own risk varies. Rates are higher with a higher starting BMI, prior abdominal surgery, and significant heart, lung, or clotting-related medical conditions. Ask Dr. Irshad how these factors apply to you.

References

  1. Chang SH, Stoll CR, Song J, et al. The Effectiveness and Risks of Bariatric Surgery: An Updated Systematic Review and Meta-analysis, 2003-2012. JAMA Surg. 2014;149(3):275–87.
  2. Flum DR, et al. (LABS Consortium). Peri-operative Safety in the Longitudinal Assessment of Bariatric Surgery. N Engl J Med. 2009;361(5):445–54.
  3. Osti N, Aboud A, Gumbs S, et al. Six-year analysis of 30-day post-operative leaks for primary sleeve gastrectomy: a MBSAQIP database study. Surg Endosc. 2024;38(12):7451–8.
  4. Bharani T, Agarwal D, Nimeri A, et al. Evaluating National Trends in Bleeding Associated with Metabolic Bariatric Surgery over 7 Years. Obes Surg. 2025;35(10):4079–86.
  5. Howard R, Chao GF, Yang J, et al. Comparative Safety of Sleeve Gastrectomy and Gastric Bypass Up to 5 Years After Surgery. JAMA Surg. 2021;156(12):1160–9.
  6. Lazzati A, Bechet S, Jouma S, et al. Revision surgery after sleeve gastrectomy: a nationwide study with 10 years of follow-up. Surg Obes Relat Dis. 2020;16(10):1497–1504. PubMed

Common questions about risk

What is the mortality rate for weight loss surgery?
Death within 30 days is very low, occurring in roughly 1 in 500 to 1 in 1,250 patients (0.08–0.2%), based on large multi-center registries and randomized trial data.
What is the leak rate after sleeve gastrectomy or gastric bypass?
A leak at a staple or connection line occurs in roughly 1 in 600 (about 0.17%) sleeve gastrectomy patients, somewhat higher for gastric bypass patients.
Will I need vitamin supplements after bariatric surgery?
Yes — a vitamin or mineral deficiency, particularly iron and vitamin B12, develops in a substantial proportion of patients over years despite taking recommended supplements, so regular blood work and lifelong supplementation are part of follow-up care.
How often is a second (revision) surgery needed after weight loss surgery?
Roughly 3% (sleeve) to 1.5% (bypass) of patients need a revision operation by 5 years, rising further with longer follow-up — up to roughly 12% by 10 years in some registries.
This page is general information, not medical advice or a consent form. It does not replace the individualized consent discussion you will have with Dr. Irshad, which accounts for your own health, anatomy, and the specific operation planned. If you are experiencing a medical emergency, call 911 or go to your nearest Emergency Department immediately. Published in compliance with the CPSO Advertising Standards Policy.

Questions about your risk?

Dr. Kashif Irshad — Division of Thoracic Surgery, William Osler Health System, Brampton Civic Hospital. Tel: (905) 458-4520 · Fax: (905) 458-4080 · thoracic@williamoslerhs.ca

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