The SAGES MASTERS program bariatric surgery pathway selects 10 seminal publications on adjustable gastric banding.

BACKGROUND: Bariatric surgery is one of the clinical pathways of the Society of American Gastrointestinal and Endoscopic Surgeons (SAGES) Masters Program, and laparoscopic adjustable gastric banding (LAGB) is one of the three anchoring bariatric procedures. To improve surgeon lifelong learning, the Masters Program seeks to identify sentinel articles of each of the 3 bariatric anchoring procedures. In this article, we present the top 10 articles on LAGB. METHODS: A systematic literature search of papers on LAGB was completed, and publications with the most citations and citation index were selected and shared with SAGES Metabolic and Bariatric Surgery Committee members for review. The individual committee members then ranked these papers, and the top 10 papers were chosen based on the composite ranking. RESULTS: The top 10 sentinel publications on LAGB contributed substantially to the body of literature related to the procedure, whether for surgical technique, novel information, or outcome analysis. A summary of each paper including expert appraisal and commentary is presented here. CONCLUSION: These seminal articles have had significant contribution to our understanding and appreciation of the LAGB procedure. Bariatric surgeons should use this resource to enhance their continual education and acquisition of specialized skills.

The SAGES MASTERS program bariatric surgery pathway selects 10 seminal publications on revisional bariatrics.

BACKGROUND: The Society of American Gastrointestinal and Endoscopic Surgeons (SAGES) Masters Program designated bariatric surgery as a clinical pathway. Among the tiers of the Masters Program, revisional bariatric surgery is the highest tier of "mastery" within the pathway. This article presents the top 10 seminal studies representing the current landscape of revisional bariatrics. METHODS: The literature was systematically searched and seminal articles designated by consensus agreement of the SAGES Metabolic and Bariatric Surgery committee using multiple criteria, including impact on the field, citation frequency, and expert opinion. Articles were reviewed by committee members and presented in summarized fashion. RESULTS: The top 10 papers are presented in grouped thematic categories covering the early evolution of revisional bariatrics, changing criteria for reoperative bariatric surgery, divergence of revision versus conversion bariatric surgery, and recent technologic innovations in revisional bariatric surgery. Each summary is presented with expert appraisal and commentary. CONCLUSION: These seminal papers represent a snapshot of the dynamic field of revisional bariatric surgery and emphasize the need to not only remain current with contemporary trends but also keep a patient-oriented perspective on patient and intervention selection for optimal success.

Human serous cavity macrophages and dendritic cells possess counterparts in the mouse with a distinct distribution between species.

In mouse peritoneal and other serous cavities, the transcription factor GATA6 drives the identity of the major cavity resident population of macrophages, with a smaller subset of cavity-resident macrophages dependent on the transcription factor IRF4. Here we showed that GATA6+ macrophages in the human peritoneum were rare, regardless of age. Instead, more human peritoneal macrophages aligned with mouse CD206+ LYVE1+ cavity macrophages that represent a differentiation stage just preceding expression of GATA6. A low abundance of CD206+ macrophages was retained in C57BL/6J mice fed a high-fat diet and in wild-captured mice, suggesting that differences between serous cavity-resident macrophages in humans and mice were not environmental. IRF4-dependent mouse serous cavity macrophages aligned closely with human CD1c+CD14+CD64+ peritoneal cells, which, in turn, resembled human peritoneal CD1c+CD14-CD64- cDC2. Thus, major populations of serous cavity-resident mononuclear phagocytes in humans and mice shared common features, but the proportions of different macrophage differentiation stages greatly differ between the two species, and dendritic cell (DC2)-like cells were especially prominent in humans.

Endoscopic Management of Gastric Band Erosion: a Systematic Review and Meta-Analysis.

BACKGROUND: Gastric band erosion may be seen in up to 3% of patients. Endoscopic intervention has become increasingly utilized due to its minimally invasive nature. The purpose of this study was to perform a systematic review and meta-analysis to examine the role of endoscopic removal for eroded gastric bands. METHODS: Individualized search strategies were developed for PubMed, EMBASE, Web of Science, and Cochrane Library databases in accordance with PRISMA and MOOSE guidelines. Outcomes included technical success, clinical success, procedure duration, adverse events, and surgical conversion. Pooled proportions were analyzed using random effects models. Heterogeneity and publication bias was assessed with I2 statistics and funnel plot asymmetry using Egger and Begg tests. Meta-regression was also performed comparing outcomes by endoscopic tools. RESULTS: Ten studies (n=282 patients) were included in this meta-analysis. Mean age was 40.68±7.25 years with average duration of band placement of 38.49±19.88 months. Pre-operative BMI was 42.76±1.06 kg/m2 with BMI of 33.06±3.81 kg/m2 at time of band erosion treatment. Endoscopic removal was attempted in 240/282 (85.11%) of cases. Pooled technical and clinical success of the endoscopic therapy was 86.08% (95% CI: 79.42-90.83; I2=28.62%) and 85.34% (95% CI: 88.70-90.62; I2=38.56%), respectively. Mean procedure time for endoscopic removal was 46.47±11.52 min with an intra-operative adverse event rate of 4.15% (95% CI: 1.98-8.51; I2=0.00%). Post-procedure-associated adverse events occurred in 7.24% (CI: 4.46-11.55; I2=0.00%) of patients. Conversion to laparotomy/laparoscopy occurred in 10.54% (95% CI: 6.12-17.54) of cases. CONCLUSION: Endoscopic intervention is a highly effective and safe modality for the treatment of gastric band erosion.

Reflux Symptoms Increase Following Sleeve Gastrectomy Despite Triage of Symptomatic Patients to Roux-en-Y Gastric Bypass.

BACKGROUND AND AIMS: Bariatric surgical options in obese patients include sleeve gastrectomy (SG) and roux-en-Y gastric bypass (RYGB), which may not be equivalent in risk of postoperative reflux symptoms. We evaluated risk and predictive factors for postbariatric surgery reflux symptoms. METHODS: Patients with obesity evaluated for bariatric surgery over a 15-month period were prospectively followed with validated symptom questionnaires (GERDQ, dominant symptom index: product of symptom frequency and intensity from 5-point Likert scores) administered before and after SG and RYGB. Esophageal testing included high-resolution manometry in all patients, and ambulatory reflux monitoring off therapy in those with abnormal GERDQ or prior reflux history. Univariate comparisons and multivariable analysis were performed to determine if preoperative factors predicted postoperative reflux symptoms. RESULTS: Sixty-four patients (median age 49.0 years, 84% female, median BMI 46.5 kg/m 2 ) fulfilled inclusion criteria and underwent follow-up assessment 4.4 years after bariatric surgery. Baseline GERDQ and dominant symptom index for heartburn were significantly higher in RYGB patients ( P ≤0.04). Despite this, median GERDQ increased by 2 (0.0 to 4.8) following SG and decreased by 0.5 (-1.0 to 5.0) following RYGB ( P =0.02). GERDQ became abnormal in 43.8% after SG and 18.8% after RYGB ( P =0.058); abnormal GERDQ improved in 12.5% and 37.5%, respectively ( P =0.041). In a model that included age, gender, BMI, acid exposure time, and type of surgery, multivariable analysis identified SG as an independent predictor of postoperative heartburn (odds ratio 16.61, P =0.024). CONCLUSIONS: Despite preferential RYGB when preoperative GERD was identified, SG independently predicted worsening heartburn symptoms after bariatric surgery.

Does gender affect experiences in the operating room for surgeons and anesthesiologists at a large academic center?

BACKGROUND: Although the number of women medical trainees has increased in recent years, they remain a minority of the academic workforce. Gender-based implicit biases may lead to deleterious effects on surgical workforce retention and productivity. METHODS: All 440 attending surgeons and anesthesiologists employed at our institution were invited to complete a survey regarding perceptions of the perioperative work environment and resources. Odds ratios for dichotomous variables were calculated using logistic regressions, and for trichotomous variables, polytomous regressions. RESULTS: 243 participants (55.2%) provided complete survey responses. Relative to men, women faculty reported a greater need to prove themselves to staff; less respect and fewer resources and opportunities; more frequent assumptions about their capabilities; and a greater need to adjust their demeanor to connect with their team (p â€‹< â€‹0.05). CONCLUSION: Perceived gender bias remains present in the perioperative environment. We need greater efforts to address barriers and create an equitable work environment.

Steatosis drives monocyte-derived macrophage accumulation in human metabolic dysfunction-associated fatty liver disease.

Background & Aims: Metabolic dysfunction-associated fatty liver disease (MAFLD) is a common complication of obesity with a hallmark feature of hepatic steatosis. Recent data from animal models of MAFLD have demonstrated substantial changes in macrophage composition in the fatty liver. In humans, the relationship between liver macrophage heterogeneity and liver steatosis is less clear. Methods: Liver tissue from 21 participants was collected at time of bariatric surgery and analysed using flow cytometry, immunofluorescence, and H&E microscopy. Single-cell RNA sequencing was also conducted on a subset of samples (n = 3). Intrahepatic triglyceride content was assessed via MRI and tissue histology. Mouse models of hepatic steatosis were used to investigate observations made from human liver tissue. Results: We observed variable degrees of liver steatosis with minimal fibrosis in our participants. Single-cell RNA sequencing revealed four macrophage clusters that exist in the human fatty liver encompassing Kupffer cells and monocyte-derived macrophages (MdMs). The genes expressed in these macrophage subsets were similar to those observed in mouse models of MAFLD. Hepatic CD14+ monocyte/macrophage number correlated with the degree of steatosis. Using mouse models of early liver steatosis, we demonstrate that recruitment of MdMs precedes Kupffer cell loss and liver damage. Electron microscopy of isolated macrophages revealed increased lipid accumulation in MdMs, and ex vivo lipid transfer experiments suggested that MdMs may serve a distinct role in lipid uptake during MAFLD. Conclusions: The human liver in MAFLD contains macrophage subsets that align well with those that appear in mouse models of fatty liver disease. Recruited myeloid cells correlate well with the degree of liver steatosis in humans. MdMs appear to participate in lipid uptake during early stages of MALFD. Impact and implications: Metabolic dysfunction associated fatty liver disease (MAFLD) is extremely common; however, the early inflammatory responses that occur in human disease are not well understood. In this study, we investigated macrophage heterogeneity in human livers during early MAFLD and demonstrated that similar shifts in macrophage subsets occur in human disease that are similar to those seen in preclinical models. These findings are important as they establish a translational link between mouse and human models of disease, which is important for the development and testing of new therapeutic approaches for MAFLD.

National Trends in Pediatric Metabolic and Bariatric Surgery: 2010-2017.

BACKGROUND: The childhood obesity epidemic has grown exponentially and is known to disproportionately affect minority groups. Successful treatment of this complex health issue requires a multidisciplinary approach including metabolic and bariatric surgery (MBS) for qualifying pediatric patients. This study examines current national trends in pediatric bariatric surgery from 2010 to 2017 using the National Inpatient Sample. METHODS: This study analyzed MBS among pediatric patients <19 years old using weighted discharge data from 2010 to 2017. The primary outcome was national procedure rates. Secondary analyses included procedure type, demographics, BMI, comorbidities, length of stay, and complication rates. RESULTS: From 2010 to 2017, annual bariatric procedure rates increased from 2.29 to 4.62 per 100 000 (P < .001). Laparoscopic sleeve gastrectomy outpaced Roux-en-Y gastric bypass and laparoscopic adjustable gastric band over time (0.31-3.99 per 100 000, P < .0001). The mean age was stable over time 18.10-17.96 (P = .78). The cohort was primarily female (76.5% to 75.4%), white (54.0% to 45.0%), and privately-insured (59.9% to 53.4%). Preoperative BMI increased from 2010 to 2017 (P < .001), whereas number of obesity-related comorbidities was stable (P > .05). Length of stay was <2 days (2.02-1.75, P = .04) and in-hospital complication rates were low (7.2% to 6.45%, P = .88). CONCLUSIONS: Pediatric MBS is underutilized nationally with disproportionately lower rates among minority groups. Despite incremental progress, further investigation into the racial and social determinants that limit access to pediatric weight loss surgery is critical.

National Trends and Outcomes in Adolescents Undergoing Bariatric Surgery.

BACKGROUND: In the US, obesity continues to be a severe health issue now affecting adolescents. Bariatric surgery remains the most effective treatment for obesity, but use among adolescents remains low. The objective of this study was to identify current national trends in bariatric surgery among adolescents. STUDY DESIGN: Using the Nationwide Inpatient Sample database, adolescents aged 9 to 19 with a diagnosis of morbid obesity who underwent a laparoscopic gastric bypass (Roux-en-Y gastric bypass) or laparoscopic sleeve gastrectomy (SG) between 2015 and 2018 were identified. Demographics, comorbidities, and in-hospital complications were collected. National estimates were calculated. The trend of annual number of operations was determined by Kruskal-Wallis rank test. RESULTS: Between 2015 and 2018, 1,203 adolescents were identified, resulting in a nationwide estimate of 4,807 bariatric cases. The number of bariatric operations increased annually from 1,360 in 2015 to 1,740 operations in 2018 (p = 0.0771). The majority of patients were female (76%), 17 to 19 years old (84.1%), and White (47.9%). Most patients underwent SG (82.0%). Black and Hispanic patients comprised 40.2% of the cohort. Significant comorbidities included diabetes, dyslipidemia, nonalcoholic fatty liver disease, hypertension, and sleep apnea. The average length of stay decreased from 2.12 days to 1.64 days. There were no in-hospital mortalities, and complications were less than 1%. CONCLUSIONS: With the increasing prevalence of obesity among adolescents in the US, bariatric surgery increased over time but was performed less in patients younger than 16 years of age and racial minorities. Bariatric surgery among adolescents remains safe, with extremely low complication rates and zero in-hospital mortality.

Trends in risk factors for readmission after bariatric surgery 2015-2018.

BACKGROUND: Readmission after bariatric surgery is multifactorial. Understanding the trends in risk factors for readmission provides opportunity to optimize patients prior to surgery identify disparities in care, and improve outcomes. OBJECTIVES: This study compares trends in bariatric surgery as they relate to risk factors for all-cause readmission. SETTING: Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) participating facilities. METHODS: The Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program database was used to analyze 760,076 bariatric cases from 854 centers. Demographics and 30-day unadjusted outcomes were compared between laparoscopic adjustable gastric banding (LAGB), sleeve gastrectomy (LSG), and Roux-en-Y gastric bypass (RYGB) performed between 2015 and 2018. A multiple logistic regression model determined predictors of readmission. RESULTS: A total of 574,453 bariatric cases met criteria, and all-cause readmission rates decreased from 4.2% in 2015 to 3.5% in 2018 (P < .0001). The percentage of non-Hispanic Black adults who underwent bariatric surgery increased from 16.7% of the total cohort in 2015 to 18.7% in 2018 (P < .0001). The percentage of Hispanic adults increased from 12.1% in 2015 to 13.8% in 2018 (P < .0001). The most common procedure performed was the LSG (71.5%), followed by RYGB (26.9%) and 1.6% LAGB (1.6%) (P < .0001). Men were protected from readmission compared with women (odds ratio [OR]: .87; 95% confidence interval [CI]: .84-.90). Non-Hispanic Black (OR: 1.52; 95% CI: 1.47-1.58)] and Hispanic adults (OR: 1.14; 95% CI: 1.09-1.19) were more likely to be readmitted compared with non-Hispanic White adults. LSG (OR: 1.27; 95% CI: 1.10-1.48) and RYGB (OR: 2.24; 95% CI: 1.93-2.60) were predictive of readmission compared with LAGB. CONCLUSION: Readmission rates decreased over 4 years. Women, along with non-Hispanic Black and Hispanic adults, were more likely to be readmitted. Future research should focus on gender and racial disparities that impact readmission.

Infection prevention plan to decrease surgical site infections in bariatric surgery patients.

BACKGROUND: Surgical site infections (SSI) are one of the most common complications of bariatric surgery. The Metabolic and Bariatric Surgery Accreditation and Quality Improvement (QI) Program (MBSAQIP) allows accredited programs to develop processes for quality improvement based on data collection. The objective of this study was to decrease SSI rates in patients undergoing bariatric surgery at an accredited MBSAQIP center. METHODS: Using the MBSAQIP semiannual report, SSI rates were retrospectively reviewed. Baseline SSI rates were collected from 01/01/2014-12/31/2015. On 01/01/2016, the first infection prevention protocol (IPP-1) was created that included 4% chlorhexidine gluconate (CHG) showers, CHG wipes immediately prior to surgery, and routine cultures of SSIs. An updated IPP (IPP-2) was implemented on 09/01/2016, which discontinued routine surgical drain placement and broadened antibiotic coverage for penicillin allergic patients. RESULTS: During baseline data collection, SSI rates were 5.1%. After the implementation of IPP-1, SSI rates trended down to 2.5%. After implementation of IPP-2, SSI rates decreased significantly to 1.5%, a 66% relative risk reduction in SSIs from baseline. On multivariate regression analysis, the perioperative factors associated with an increased risk for SSIs included diabetes mellitus, intraoperative surgical drain placement, the number of hypertension medications prior to bariatric surgery, and an open approach. CONCLUSIONS: Our study demonstrates that the implementation of a specific protocol for reducing SSIs is safe and feasible in patients undergoing bariatric surgery. We also identified that the success of the IPP is likely centered on the elimination of routine drain placement during primary bariatric procedures.

10-year weight loss outcomes after Roux-en-Y gastric bypass and attendance at follow-up visits: a single-center study.

BACKGROUND: Long-term durability of weight loss is a prerequisite for a greater acceptance of bariatric surgery. OBJECTIVES: To examine long-term weight trajectory in patients undergoing Roux-en-Y gastric bypass (RYGB) and determine factors predicting long-term follow-up and weight outcomes. SETTING: University hospital. METHODS: A retrospective cohort of adults who underwent RYGB during 1997-2010 were identified and followed until 2017. Predictors for attendance at periodic follow-up visits, reduction in body mass index (BMI), and percent excess BMI lost were determined using multivariable logistic regression and linear mixed-effects models. The latter was used to predict long-term weight outcomes for a typical patient. RESULTS: The study included 1104 patients with a mean age of 45.5 (standard deviation [SD] 9.9) years and a preoperative BMI of 54.7 (SD 10.9) kg/m2. Follow-up data were available for 92.8% of the patients after 1 year, 50.0% after 5 years, and 35.2% after 10 years post-surgery. Black patients, compared with White patients, were less likely to attend follow-up visits. Attendance at follow-up visits at least every other year was not associated with larger weight loss, but higher preoperative BMI, being White (versus Black), and female sex were. Predicted BMI reduction for a typical patient, a 45-year-old White female with a preoperative BMI of 54.7 kg/m2 and private health insurance, undergoing laparoscopic RYGB in 2004, was 18.3 (standard error [SE] .36) kg/m2 at year 5 and 17.6 (SE .49) kg/m2 at year 10. CONCLUSION: RYGB results in clinically significant and durable weight loss. Attendance at periodic follow-up visits does not appear to be associated with long-term weight loss outcomes. Future work should focus on strategies to remove barriers to post-operative care.

Reducing Operating Room Cost: Comparing Attending and Surgical Trainee Perceptions About the Implementation of Supply Receipts.

BACKGROUND: As operating room (OR) expenditures increase, faculty and surgical trainees will play a key role in curbing future costs. However, supply cost utilization varies widely among providers and, despite requirements for cost education during surgical training, little is known about trainees' comfort discussing these topics. To improve OR cost transparency, our institution began delivering real-time supply "receipts" to faculty and trainees after each surgical case. This study compares faculty and surgical trainees' perceptions about supply receipts and their effect on individual practice and cultural change. STUDY DESIGN: Faculty and surgical trainees (residents and fellows) from all adult surgical specialties at a large academic center were emailed separate surveys. RESULTS: A total of 120 faculty (30.0% response rate) and 119 trainees (35.7% response rate) completed the survey. Compared with trainees, faculty are more confident discussing OR costs (p < 0.001). Two-thirds of trainees report discussing OR costs with faculty as opposed to 77.0% of faculty who acknowledge having these conversations (p = 0.08). Both groups showed a strong commitment to reduce OR expenditures, with 87.3% of faculty and 90.0% of trainees expressing a responsibility to curb OR costs (p = 0.84). After 1 year of implementation, faculty continue to have high interest levels in supply receipts (82.4%) and many surgeons review them after each case (67.7%). In addition, 74.3% of faculty are now aware of how to lower OR costs and 52.5% have changed the OR supplies they use. Trainees, in particular, desire additional cost-reducing efforts at our institution (p < 0.001). CONCLUSIONS: Supply receipts have been well received and have led to meaningful cultural changes. However, trainees are less confident discussing these issues and desire a greater emphasis on OR cost in their curriculum.

Understanding the Current Role of Robotic-Assisted Bariatric Surgery.

BACKGROUND: The role of robotic surgery in bariatrics remains controversial. Patient selection for robotic surgery is not well-studied. The objective of this study was to identify factors associated with robotic surgery and its temporal trends. METHODS: The Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program database from 2015 to 2018 was used. Adult patients undergoing primary sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB) using the laparoscopic or robotic approach were identified. Revisional, hybrid, or those with concomitant procedures were excluded. Logistic regression was conducted to identify factors associated with undergoing robotic-assisted surgery. RESULTS: Among 211,568 patients who underwent SG, 9.1% underwent a robotic SG; among 76,805 patients who underwent RYGB, 7.9% of patients underwent a robotic RYGB. During 2015-2018, robotics increased from 7.1 to 11.3% for SG and 7.4 to 8.6% for RYGB. After controlling for patient characteristics, there was still an increasing trend in the use of robotic surgery: SG (multivariable-adjusted odds ratio, aOR, 1.18; 95% confidence interval, CI, 1.17-1.20) and RYGB (aOR, 1.05; 95% CI, 1.03-1.08). For both robotic SG and RYGB, functional status and African American race were associated with undergoing robotic surgery, while races other than White or African American and Hispanic ethnicity were not. Pre-operative IVC filter was associated with robotic SG, while the presence of GERD, diabetes, and COPD were associated with robotic RYGB. CONCLUSIONS: Robotic bariatric surgery has increased over time. Our findings identified factors associated with the receipt of robotic surgery. Reasons for these factors require further investigation to better delineate indications for this technology.

Initial Experience with a Virtual Platform for Advanced Gastrointestinal Minimally Invasive Surgery Fellowship Interviews.

BACKGROUND: The COVID-19 pandemic travel restrictions triggered a rapid alteration in the interview process for fellowships this spring. We describe our initial experience with virtual interviews for Advanced Gastrointestinal (GI) Minimally Invasive Surgery Fellowships and assess the value and limitations via a post-interview applicant survey. STUDY DESIGN: Twenty candidates were interviewed via Zoom teleconferencing during March and April 2020 using combined group and breakout rooms. An anonymous post-interview Likert and free text survey was sent to candidates with questions regarding feasibility, appropriateness, and acceptability of this method. RESULTS: Seventeen of 20 candidates (85%) responded to the survey. The candidates rated ease of interaction with the program director, faculty surgeons, and the current fellow highly: 94%, 83%, and 89%, respectively. The majority (53%) stated the virtual interviews exceeded or met expectations. Only a minority, 12%, reported the virtual platform was short of expectations. Approximately 70% noted little to no impact of not being able to conduct these interviews in-person and not being able to physically see the program institution. Overall, 94% were satisfied with their experience, and only 6% were neutral, with no respondents reporting dissatisfaction. Finally, 76% would recommend a virtual interview in the future. Most negative open response comments were secondary to issues with software rather than the lack of the in-person traditional interviews. CONCLUSIONS: The use of a remote teleconferencing platform provides a favorable method for conducting fellowship interviews and results in a high degree of candidate satisfaction. Virtual interviews will likely be increasingly substituted for in-person interviews across the spectrum of medical training.

Effects of Diet versus Gastric Bypass on Metabolic Function in Diabetes.

BACKGROUND: Some studies have suggested that in people with type 2 diabetes, Roux-en-Y gastric bypass has therapeutic effects on metabolic function that are independent of weight loss. METHODS: We evaluated metabolic regulators of glucose homeostasis before and after matched (approximately 18%) weight loss induced by gastric bypass (surgery group) or diet alone (diet group) in 22 patients with obesity and diabetes. The primary outcome was the change in hepatic insulin sensitivity, assessed by infusion of insulin at low rates (stages 1 and 2 of a 3-stage hyperinsulinemic euglycemic pancreatic clamp). Secondary outcomes were changes in muscle insulin sensitivity, beta-cell function, and 24-hour plasma glucose and insulin profiles. RESULTS: Weight loss was associated with increases in mean suppression of glucose production from baseline, by 7.04 µmol per kilogram of fat-free mass per minute (95% confidence interval [CI], 4.74 to 9.33) in the diet group and by 7.02 µmol per kilogram of fat-free mass per minute (95% CI, 3.21 to 10.84) in the surgery group during clamp stage 1, and by 5.39 (95% CI, 2.44 to 8.34) and 5.37 (95% CI, 2.41 to 8.33) µmol per kilogram of fat-free mass per minute in the two groups, respectively, during clamp stage 2; there were no significant differences between the groups. Weight loss was associated with increased insulin-stimulated glucose disposal, from 30.5±15.9 to 61.6±13.0 µmol per kilogram of fat-free mass per minute in the diet group and from 29.4±12.6 to 54.5±10.4 µmol per kilogram of fat-free mass per minute in the surgery group; there was no significant difference between the groups. Weight loss increased beta-cell function (insulin secretion relative to insulin sensitivity) by 1.83 units (95% CI, 1.22 to 2.44) in the diet group and by 1.11 units (95% CI, 0.08 to 2.15) in the surgery group, with no significant difference between the groups, and it decreased the areas under the curve for 24-hour plasma glucose and insulin levels in both groups, with no significant difference between the groups. No major complications occurred in either group. CONCLUSIONS: In this study involving patients with obesity and type 2 diabetes, the metabolic benefits of gastric bypass surgery and diet were similar and were apparently related to weight loss itself, with no evident clinically important effects independent of weight loss. (Funded by the National Institutes of Health and others; ClinicalTrials.gov number, NCT02207777.).