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Weight Loss In Diabetic Patients After Bariatric Surgery

Weight Loss In Diabetic Patients After Bariatric Surgery

In recent decades, obesity and its repercussions have posed a significant healthcare challenge. Back in 2015–2016, almost 39.8% of US adults were grappling with obesity, and projections suggest a potential surge to 51% by 2030. The economic toll of obesity-related comorbidities is substantial, and the health risks for those carrying excess weight are well-documented, with a higher susceptibility to metabolic diseases and increased overall mortality.

Addressing obesity has become a top healthcare priority, emphasizing the need for comprehensive treatment approaches that can either alleviate or halt its progression and associated consequences. 

Bariatric surgery emerges as a highly effective option, showcasing favorable outcomes regarding weight loss, prevention, and remission of comorbidities. Our previous work delved into comparing outcomes between gastric bypass (GB) and sleeve gastrectomy (SG) within our Michigan Bariatric Surgery Cohort (MI‐BASiC) in years 2 and 4. As observed in various studies, GB tends to outshine SG in terms of weight loss and achieving remission rates for conditions like diabetes, hypertension, and dyslipidemia.

Their focus transitioned to the nuanced variations in weight loss outcomes among individuals. The aim was to unravel the impact of baseline comorbidities on the extent of postoperative weight loss. 

While some studies hinted at the detrimental influence of baseline diabetes on ultimate weight loss, their investigation specifically sought to quantify how diabetes affects weight loss outcomes after bariatric surgery within a larger study group. The anticipation is that this study will provide fresh insights into the intricate interplay between diabetes, obesity, and the outcomes of bariatric surgery.

Study Summary 

Bariatric surgery has shown promise in resolving obesity and diabetes in patients. Yet, the specific influence of diabetes on the extent of weight loss following the procedure remains uncertain and has not been accurately measured.

Research Design and Methods

The study examined the impact of baseline diabetes on weight loss outcomes using data extracted from the Michigan Bariatric Surgery Cohort (MI‐BASiC). The inclusion criteria comprised consecutive patients aged 18 and above who underwent gastric bypass (GB) or sleeve gastrectomy (SG) for obesity at the University of Michigan between January 2008 and November 2013. Repeated measures analysis was employed to assess whether diabetes functioned as a predictor of weight loss outcomes over the 5-year post-surgery period.


The Michigan Bariatric Surgery Cohort (MI‐BASiC) included 714 patients aged 18 and older undergoing gastric bypass (GB) or sleeve gastrectomy (SG) for obesity at the University of Michigan between January 2008 and November 2013. 

Data Collection

Within the multidisciplinary University of Michigan Adult Bariatric Surgery Program, a systematic approach governs patient engagement. Preoperative evaluations set the stage, followed by postoperative monitoring involving surgeons and dietitians at 2 weeks and 2 months. 

Definitions and Time of Follow‐Up:

Total weight loss (TWL) was the disparity between pre-surgery and post-surgery weights, expressed as TWL percent (TWL%). Excess weight (EW) was the difference between initial and ideal weight, with EW loss percent (EWL%) calculated as the percentage of TWL to EW. Weight regain (WR) was computed from the minimum recorded weight, with three definitions for significant WR. 

Statistical Analysis

Continuous data were presented as mean ± standard error, and categorical data as counts and percentages. Baseline characteristics between gastric bypass (GB) and sleeve gastrectomy (SG) groups were compared using appropriate tests. Repeated measures analyses assessed weight-related outcomes over 5 years, considering potential covariates. Odds ratios were calculated for binary outcomes, with missing data addressed through imputation. Significance was set at p< .05. SAS (version 9.4) facilitated statistical analyses.


Among the 714 patients included in the study, 380 underwent gastric bypass (GB) [mean BMI 47.3 ± 0.4 kg/m2, diabetes 149 (39.2%)] and 334 had sleeve gastrectomy (SG) [mean BMI 49.9 ± 0.5 kg/m2, diabetes 108 (32.3%)]. The findings from multivariable repeated measures analysis, adjusting for covariates, revealed that individuals with diabetes exhibited a significantly lower percentage of total weight loss (p= .0023) and excess weight loss (p= .0212) compared to those without diabetes.

In their study, the primary objective was to assess the influence of baseline comorbidities, particularly diabetes, on eventual weight loss. Preceding the presentation of these findings, the authors briefly outlined the cohort’s overall responses, consistent with their previously published 4‐year follow‐up results. Weight loss outcomes and metabolic improvements at 5 years mirrored those at 4 years.

In the study population, successful weight loss occurred in 33.4%, primary nonresponse in 27.2%, and secondary nonresponse in 39.4% over 5 years. The percentage without diabetes increased linearly from primary nonresponse (58.4%) to secondary nonresponse (64.9%) to successful weight loss (66.2%). 

This trend was not observed for those without hypertension or dyslipidemia, indicating the potential significance of baseline diabetes in final weight loss outcomes. Further analysis comparing diabetes presence in the two surgery types revealed differences in clinical characteristics.

Diabetic patients were older, had more males, and presented with more comorbidities. They exhibited higher HbA1c and lower HDL levels but lower total and LDL cholesterol due to dyslipidemia treatment guidelines. 

In the total group, diabetic patients were older (48.8 ± 9.5 vs. 41.9 ± 11.1), included more males (28.2% vs. 16.6%), and had higher baseline HbA1c levels (7.22 ± 0.1 vs. 5.73 ± 0.02). However, there were no differences in SBP. These findings emphasized the potential impact of baseline diabetes on weight loss outcomes and warranted further investigation.

Final Thoughts

The study’s aim was to evaluate the influence of diabetes on overall weight loss following gastric bypass (GB) and sleeve gastrectomy (SG) in a substantial cohort of over 700 patients. The study’s findings reveal that individuals with diabetes undergo less weight loss compared to those without diabetes after bariatric surgery, a distinction noticeable from the first year of follow‐up and sustained over an extended period. 

Notably, diabetes exerts a more pronounced impact on weight loss outcomes following GB than SG in our dataset. These outcomes suggest that individuals with diabetes should adjust their expectations regarding weight loss outcomes when considering bariatric surgery. This study, one of the first and largest real-world investigations to address this question, spans a 5-year duration with a sizable sample size, encompassing both Roux-en-Y gastric bypass (RYGB) and SG procedures. 

While bariatric surgery’s primary clinical impact for patients with obesity and diabetes is diabetes remission, understanding the projected weight loss before surgery and the factors influencing it is crucial for each patient. This study contributes valuable information for both surgeons and patients, potentially impacting clinical decisions and discussions around bariatric surgery. Furthermore, the observations prompt a consideration of bariatric surgery before the onset of diabetes to optimize weight loss outcomes, offering perspectives that could significantly influence patient counseling and healthcare decisions.

In summary, the data presented in the study indicate that the presence of diabetes hampers the weight loss outcomes of bariatric surgery, particularly within the initial 3 years post-surgery, notably in individuals opting for gastric bypass (GB). The findings suggest that individuals with diabetes might consider Roux-en-Y gastric bypass (RYGB) over sleeve gastrectomy to optimize weight loss at the 5-year mark. 

Although the underlying mechanisms are currently unclear, these results carry practical implications. Tailoring expectations differently for patients with established diabetes compared to those without, and contemplating surgical interventions for obesity earlier in the comorbidity progression scale or intensifying treatment strategies post-surgery in those with established diabetes, becomes crucial.

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