Highlights
This multicenter retrospective cohort study represents one of the largest investigations into metabolic bariatric surgery (MBS) outcomes specifically among adults with type 1 diabetes (T1D) and obesity. The findings demonstrate remarkable metabolic improvements: participants achieved a mean total weight loss of 29.7% at one year, reduced daily insulin requirements by 57%, and experienced significant improvements across multiple cardiometabolic parameters. These results challenge conventional assumptions about surgical intervention in T1D and open new avenues for integrated metabolic management strategies.
Background: The Dual Challenge of Type 1 Diabetes and Obesity
Type 1 diabetes and obesity represent a increasingly common clinical paradox. Historically, type 1 diabetes was characterized by a phenotype of relative leanness, yet the contemporary obesity epidemic has fundamentally altered this landscape. Approximately one-third of individuals with T1D now meet criteria for obesity, driven by factors including intensive insulin therapy, sedentary lifestyles, and shared genetic susceptibility to metabolic dysfunction. This dual diagnosis creates a particularly challenging clinical scenario: patients face the persistent autoimmune destruction of pancreatic beta cells while simultaneously grappling with insulin resistance and its associated cardiovascular risks.
The management of T1D in the context of obesity presents unique therapeutic dilemmas. Higher insulin requirements correlate with weight gain, which in turn exacerbates insulin resistance—a vicious cycle that complicates glycemic control and accelerates microvascular and macrovascular complications. Furthermore, individuals with T1D and obesity experience disproportionate rates of hypertension, dyslipidemia, and cardiovascular disease, creating a compounding burden of morbidity.
Metabolic bariatric surgery has emerged as a powerful intervention for obesity and its metabolic comorbidities in the general population. Procedures such as Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) induce substantial weight loss and metabolic improvements through mechanisms beyond simple caloric restriction, including hormonal changes, gut microbiome alterations, and bile acid metabolism modifications. However, the application of MBS to individuals with type 1 diabetes has remained controversial and understudied, largely due to the autoimmune pathophysiology of T1D, which fundamentally differs from the insulin resistance-based mechanisms typically addressed by bariatric surgery.
The critical question addressed by van der Meer and colleagues centers on whether the metabolic benefits of bariatric surgery extend to individuals whose diabetes stems from insulin deficiency rather than insulin resistance. This distinction carries profound implications for patient selection, surgical timing, and expectations regarding glycemic outcomes.
Study Design and Methods
This multicenter retrospective cohort study collected data from specialized bariatric surgery centers across Europe, including Belgium, the Netherlands, and Kuwait. The study population comprised 162 adults diagnosed with type 1 diabetes and obesity (defined as BMI ≥30 kg/m²) who underwent metabolic bariatric surgery. Surgical procedures included sleeve gastrectomy, Roux-en-Y gastric bypass, and biliopancreatic diversion with duodenal switch, selected based on individualized clinical assessment and patient preference.
The primary endpoints assessed included total percentage weight loss, changes in daily insulin requirements (expressed as units per kilogram of body weight per day), and glycated hemoglobin (HbA1c) levels. Secondary endpoints encompassed a comprehensive cardiometabolic panel including LDL cholesterol, HDL cholesterol, total cholesterol, and triglycerides. Assessments were performed at baseline (prior to surgery) and at one-year follow-up, with additional longitudinal data collected to identify determinants of treatment response.
Statistical analyses employed longitudinal regression models to assess pre-to-post surgical changes and to identify factors associated with differential treatment response. Given the retrospective nature of the study, adjustments were made for potential confounding variables, though the authors acknowledge inherent limitations in observational data collection.
Key Findings
Weight Loss Outcomes
The study demonstrated substantial and clinically meaningful weight loss following metabolic bariatric surgery. At one year post-surgery, participants achieved a mean total weight loss percentage of 29.7%, with a remarkably narrow interquartile range (IQR) of 29.4% to 30.3%. This consistency in weight loss outcomes across the cohort suggests robust efficacy of MBS in this population, regardless of the specific surgical procedure performed or baseline patient characteristics.
The magnitude of weight loss substantially exceeds what is typically achievable with lifestyle interventions or pharmacological weight management in individuals with T1D, where insulin-induced weight gain and metabolic inflexibility present persistent challenges. A 30% total body weight loss represents a threshold associated with meaningful improvements in obesity-related comorbidities, including obstructive sleep apnea, non-alcoholic fatty liver disease, and cardiovascular risk reduction.
Insulin Requirement Reduction
Perhaps the most striking finding concerns insulin requirements, which represent a critical driver of weight gain, hypoglycemia risk, and healthcare costs in T1D management. Baseline insulin requirements averaged 0.75 units/kg/day (IQR: 0.58, 1.00), reflecting the combined effects of insulin deficiency and insulin resistance characteristic of obese T1D. One year following MBS, insulin requirements plummeted to 0.32 units/kg/day (IQR: 0.23, 0.43), representing a 57% reduction that achieved statistical significance at P < 0.001.
This dramatic reduction in insulin requirements likely reflects multiple mechanisms: decreased insulin resistance from significant weight loss, improved insulin sensitivity at the cellular level, and potential changes in insulin pharmacokinetics. The reduction in insulin dosing carries secondary benefits including decreased caloric intake from reduced exogenous insulin (which promotes lipogenesis), fewer hypoglycemic episodes, and improved quality of life.
Glycemic Control Improvements
HbA1c levels demonstrated statistically significant improvement, declining from a baseline median of 64.0 mmol/mol (IQR: 57.0, 74.0) to 60.0 mmol/mol (IQR: 53.4, 68.0) at one year (P < 0.001). While this reduction of approximately 4 mmol/mol may appear modest in absolute terms, it represents meaningful clinical progress given the challenging population. The Diabetes Control and Complications Trial established that every 10 mmol/mol reduction in HbA1c translates to approximately 25% reduction in microvascular complications, making incremental improvements highly consequential for long-term outcomes.
Notably, the glycemic response exhibited considerable heterogeneity across the cohort. Longitudinal modeling revealed that higher baseline HbA1c levels predicted poorer postsurgical glycemic control, suggesting that patients with more severe hyperglycemia at baseline may require additional support to achieve optimal outcomes. This finding has important implications for patient selection and pre-surgical optimization strategies.
Lipid Profile Improvements
The cardiometabolic benefits of MBS extended comprehensively to lipid parameters. All measured lipid fractions demonstrated statistically significant improvement at one year (P < 0.001 for all comparisons):
The improvements in LDL cholesterol, HDL cholesterol, triglycerides, and total cholesterol collectively contribute to substantial cardiovascular risk reduction. Individuals with T1D face elevated cardiovascular mortality—approximately three to four times that of the non-diabetic population—making any meaningful improvement in lipid profile carries profound implications for life expectancy and quality of life.
Determinants of Treatment Response
The longitudinal models identified two key predictors of treatment response. Greater total weight loss correlated strongly with reduced insulin requirements, suggesting that maximizing weight loss may be particularly important for optimizing insulin sensitivity outcomes. Conversely, higher baseline HbA1c emerged as a predictor of poorer postsurgical glycemic control, indicating that patients with severe baseline hyperglycemia may represent a distinct phenotype requiring intensified post-surgical management.
These findings align with the emerging understanding of T1D heterogeneity—specifically, the recognition that some individuals with T1D exhibit features of insulin resistance (sometimes termed “double diabetes”) and may derive greater benefit from metabolic interventions targeting insulin sensitivity.
Clinical Implications and Expert Commentary
The findings from van der Meer and colleagues challenge prevailing assumptions about the role of bariatric surgery in type 1 diabetes management. Traditionally, MBS has been viewed with caution in T1D due to concerns about hypoglycemia risk, nutritional deficiencies, and the belief that insulin deficiency rather than insulin resistance drives the pathophysiology. However, this study and emerging evidence suggest that metabolic surgery addresses fundamental mechanisms relevant even in autoimmune diabetes.
The dramatic reduction in insulin requirements observed—without deterioration in glycemic control—indicates improved insulin sensitivity at the tissue level. This finding has important implications for understanding T1D pathophysiology: while autoimmune beta cell destruction remains the proximate cause of insulin deficiency, insulin resistance at peripheral tissues contributes substantially to the metabolic burden in obese individuals with T1D. Addressing this component through surgical intervention yields meaningful clinical benefits.
Several important considerations warrant emphasis. First, bariatric surgery in T1D requires specialized multidisciplinary care, including endocrinology, bariatric surgery, nutrition, and diabetes technology expertise. Patients must be counseled extensively regarding the lifelong nutritional supplementation requirements, the need for close glucose monitoring during the rapid weight loss phase, and the potential for altered insulin pharmacokinetics. Second, the retrospective design limits causal inference—randomized controlled trials would provide stronger evidence but face ethical and practical challenges.
The study population included only individuals with established T1D (presumably C-peptide negative), yet the response patterns suggest meaningful metabolic benefit beyond what would be expected from weight loss alone. This observation supports ongoing investigation into the hormonal mechanisms of bariatric surgery, including changes in incretin hormones, bile acid metabolism, and gut-brain signaling, which may operate independently of insulin resistance status.
Conclusion
This multicenter retrospective cohort study provides compelling evidence that metabolic bariatric surgery offers substantial metabolic benefits for adults with type 1 diabetes and obesity. The 29.7% total weight loss, 57% reduction in insulin requirements, significant improvements in HbA1c, and comprehensive cardiometabolic optimization collectively suggest that MBS should be considered as part of the comprehensive management strategy for this high-risk population.
The findings support a paradigm shift in how clinicians approach the intersection of T1D and obesity. Rather than viewing these conditions as mutually exclusive therapeutic domains, integrated approaches recognizing the metabolic interconnections may yield superior outcomes. Future research should focus on identifying optimal patient selection criteria, comparing surgical procedures within the T1D population, and establishing long-term safety and efficacy data.
For practicing clinicians, these data provide a foundation for informed discussion with patients struggling with obesity and type 1 diabetes. While bariatric surgery is not appropriate for all patients, those with severe obesity (BMI ≥35-40 kg/m²) and inadequate glycemic control despite optimized medical therapy may be candidates for surgical referral. The substantial improvements demonstrated in this study offer hope for meaningful metabolic transformation in a population historically viewed as having limited therapeutic options beyond insulin intensification.
Funding and Disclosures
The original study was conducted as a collaborative effort across multiple European and Middle Eastern institutions. Detailed funding information and potential conflicts of interest should be referenced from the original publication in Diabetes Care (2026;49(4):658-663).
References
van der Meer R, Pazmino S, Steenackers N, van Laar A, Sluis M, Tolenaars L, Rosen J, Hurtado Del Pozo C, le Roux CW, Al Kandari J, Irshad M, Lannoo M, Deleus E, Dillemans B, Van Nieuwenhove Y, van Bon A, Hazebroek E, Al Ozairi E, Hoogma R, Mathieu C, Liem R, Van der Schueren B. Impact of Metabolic Bariatric Surgery on Weight Loss and Glycemic Control in Adults With Type 1 Diabetes: A Multicenter Retrospective Cohort Study. Diabetes Care. 2026-Apr-01;49(4):658-663. PMID: 41706050.
American Diabetes Association. Standards of Care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1):S1-S321.
National Institute for Health and Care Excellence (NICE). Obesity: identification, assessment and management. Clinical guideline CG189. Updated November 2023.
