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Study overview and headline findings
A large retrospective comparison led by researchers at New York University examined how two classes of weight-loss interventions — bariatric surgery and GLP-1 receptor agonist medications such as semaglutide (Ozempic) and tirzepatide — perform in routine clinical practice. The investigators matched patients using electronic health records by age, body mass index (BMI), and measures of blood glucose, then compared outcomes for those who underwent sleeve gastrectomy or gastric bypass against those treated with a GLP-1 prescription.
Over a two-year follow-up window the difference was substantial: patients who had bariatric surgery lost a mean of 25.7 percent of their baseline body weight, while patients prescribed semaglutide or tirzepatide lost a mean of 5.3 percent. The gap persisted across shorter time intervals in the study, with surgical patients consistently achieving greater reductions in weight and improvements in glycemic control.
The authors note two principal drivers of this gap. First, surgery produces durable anatomical and physiological changes that promote weight loss and long-term metabolic improvements. Second, adherence to GLP-1 medications in the real world is lower than in tightly controlled clinical trials; discontinuation within 12 months is common and reduces average treatment effectiveness.
Scientific background: GLP-1 drugs and bariatric procedures
Glucagon-like peptide-1 (GLP-1) receptor agonists are a class of injectable (and in some cases oral) medications that amplify signaling normally produced by the GLP-1 hormone. That signaling slows gastric emptying, reduces appetite, and enhances insulin secretion, which together can drive meaningful weight loss and better blood-sugar control. Semaglutide and tirzepatide became prominent after randomized controlled trials reported average weight reductions in the range of roughly 15 to 21 percent for some dosing regimens.
By contrast, bariatric operations such as sleeve gastrectomy and Roux-en-Y gastric bypass produce sustained anatomic and hormonal changes. These procedures reduce stomach volume, alter gut hormone profiles (including GLP-1 and other incretins), and change nutrient flow through the digestive tract — mechanisms that often produce larger and longer-lasting weight loss and metabolic improvement than pharmacotherapy alone.
Types of bariatric surgery
- Sleeve gastrectomy: surgical removal of a large portion of the stomach to limit intake and change appetite-regulating hormones.
- Roux-en-Y gastric bypass: creation of a small stomach pouch and rerouting of part of the small intestine, which reduces caloric absorption and modifies gut hormone responses.
Both procedures are considered established metabolic and bariatric surgeries and have decades of outcome data supporting their safety and efficacy when performed in experienced centers.
Adherence, real-world effectiveness, and the funding context
The NYU analysis highlights a common pattern in real-world data: outcomes achieved in randomized clinical trials are often larger than those observed in broader clinical practice. The study authors point out that while clinical trials for GLP-1 receptor agonists have reported weight loss of 15–21 percent, actual weight loss observed in electronic health records was considerably lower, even among patients with active prescriptions for a full year.
The study also draws attention to adherence: published estimates suggest up to 70 percent of patients discontinue GLP-1 therapy within 12 months. Reasons include side effects, cost, injection burden, perceived lack of benefit, or preference for an alternative approach. Because bariatric surgery is a one-time intervention with lasting anatomic changes, it avoids the need for ongoing medication adherence but introduces its own set of risks and long-term lifestyle requirements.
It is important to note potential conflicts of interest: the analysis was funded by the American Society for Metabolic and Bariatric Surgery (ASMBS), an organization with an institutional interest in promoting surgical options. The authors report that they are not discounting the clinical value of GLP-1 drugs, which remain widely prescribed and beneficial for many patients.
Clinical implications and comparative metabolic effects
Beyond weight change, both GLP-1 drugs and bariatric surgery have favorable effects on type 2 diabetes and cardiovascular risk factors. Semaglutide was initially developed and licensed for glucose control in patients with type 2 diabetes; subsequent trials and observational studies found reductions in cardiovascular events and signals for lower cancer risk in some contexts. The NYU study found that bariatric surgery was associated with even greater improvements in blood-sugar control compared with the medication group over the follow-up period.
However, greater metabolic benefit with surgery must be weighed against perioperative risk, the permanence of anatomical changes, and the need for lifelong nutritional monitoring and adherence to dietary guidance. Surgery requires experienced multidisciplinary teams to manage potential complications and long-term sequelae such as nutrient deficiencies.
Who chooses which option?
Although GLP-1 prescriptions have surged — with reported prescription volumes roughly doubling from 2022 to 2023 in some datasets — most eligible patients still do not undergo surgical treatment. Barriers to surgery include access to accredited centres, insurance coverage, patient preference, perceived invasiveness, and concerns about complications. Conversely, many patients prefer pharmacotherapy because it is less invasive and more immediately reversible.
Expert Insight
Dr. Maya Patel, MD, Endocrinologist and Clinical Researcher, offers perspective on balancing options:
'Both approaches — GLP-1 receptor agonists and bariatric surgery — have important roles in modern metabolic care. For some patients with severe obesity and uncontrolled diabetes, surgery provides remission rates and sustained weight loss that medications rarely achieve in the real world. For others, especially those who are earlier in disease progression or who prefer non-surgical treatment, GLP-1 therapy may be the right first step. Shared decision-making that factors in comorbidities, cost, access, and patient goals is essential.'
Dr. Patel also emphasizes the role of long-term support: 'Regardless of chosen treatment, multidisciplinary follow-up including nutrition, behavioral counseling, and medical monitoring is critical to maximize benefit and minimize harm.'
Limitations, unanswered questions, and research priorities
Key limitations of the NYU study reflect its retrospective design. Matching by age, BMI, and glycemic measures helps but cannot account for all differences in baseline health, patient motivation, socioeconomic variables, or reasons for treatment selection. The observational approach is vulnerable to confounding by indication: patients selected for surgery may differ systematically from those prescribed medication.
Research priorities identified by the authors and other clinicians include:
- Identifying patient subgroups most likely to benefit from surgery versus pharmacotherapy, using clinical, behavioral, and socioeconomic predictors;
- Testing interventions to boost adherence and persistence with GLP-1 treatment in real-world settings;
- Quantifying the impact of out-of-pocket costs and insurance coverage on long-term outcomes;
- Evaluating combination strategies, such as initiating GLP-1 therapy before or after surgery to optimize outcomes in selected patients.
Karan Chhabra, a bariatric surgeon at NYU Grossman School of Medicine, commented that future work will aim to 'identify what healthcare providers can do to optimize GLP-1 outcomes, identify which patients are better treated with bariatric surgery versus GLP-1s, and determine the role out-of-pocket costs play in treatment success.'
Conclusion
This large real-world comparison indicates that bariatric surgery delivers substantially greater average weight loss and superior glycemic control over two years compared with GLP-1 receptor agonist medications as observed in routine practice. GLP-1 therapies remain an important, less invasive option with demonstrable metabolic benefits and growing popularity. Treatment choice should be individualized, balancing expected efficacy, safety, patient preference, adherence likelihood, and access. Ongoing prospective studies and efforts to improve medication persistence, cost access, and patient selection will be essential to clarify how best to deploy these powerful tools in clinical care.
The research was presented at the ASMBS annual meeting 2025. An earlier version of this article was first published in June 2025.
Source: sciencealert
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