Pharmacological approaches are gaining attention, but metabolic bariatric surgery (MBS) remains an effective option for people with type 1 diabetes (T1D) and very high BMI. A study in Diabetes Care showed that one year after surgery, people experienced 30 % weight loss, 58 % reduction in insulin requirements, and significant improvements in cardiometabolic markers.

“This study really highlights that bariatric surgery is a valuable treatment option in people living with T1D and obesity,” says last author Bart Van der Schueren, University Hospital Leuven. “It provides the largest cohort of patients with T1D who have undergone bariatric surgery,” adds co-author Carel Le Roux, Diabetes Complications Research Centre, Ireland.

Data from three countries

The researchers retrospectively analysed data from 162 people with T1D and obesity before and after MBS. Three out of four participants were women, with an average BMI of 40.2 kg/m². 42 % underwent Roux-en-Y gastric bypass (RYGB), 58 % received sleeve gastrectomy (SG).

“The cohort represents several countries – Belgium, the Netherlands, and Kuwait – with different clinical practices, yet the results are consistent and the variation limited,” says Le Roux. “This allows the reader to form a good idea of how bariatric surgery will perform in their patients with T1D when treated in an expert centre.”

30 % weight loss, 58 % less insulin

Most weight loss occurred during the first months after surgery. After one year, participants had lost 29.7 % of body weight; BMI dropped to 28.5 kg/m². Weight loss did not differ significantly between RYGB and SG. At the same time, insulin requirements significantly fell by more than half from 0.75 to 0.32 units/kg/day. Greater weight loss was associated with larger reductions in insulin requirements. HbA1c improved modestly from 64.0 to 60.0 mmol/mol, while cardiometabolic markers significantly improved.

“The fact that on-average glycaemic control improved only marginally is counterbalanced by a huge improvement in cardiovascular risk factors – such as LDL, total cholesterol, triglycerides, and blood pressure – as well as weight,” says Sofía Pazmiño Lucio, co-author and postdoc at KU Leuven. “This is particularly relevant in a patient population where the residual cardiovascular burden remains high. Moreover, it seems that there was no increase in hypoglycaemic events after bariatric surgery.”

Does MBS improve insulin sensitivity?

Three months after surgery, an average weight loss of 17–18 % was associated with a 47–49 % decrease in insulin requirements. Their models suggest that every 10 % reduction in body weight corresponds to around 0.10 units/kg/day lower insulin requirements.

“The reduction in insulin requirements can be explained by reduced insulin resistance as a consequence of lower visceral and subcutaneous fat mass, reflected by the overall weight loss,” says Le Roux.

Van der Schueren cautions, however, that the relationship is not entirely straightforward: “The strong association observed between total weight loss and reduced insulin requirements can reasonably be interpreted as partly reflecting improved insulin sensitivity, and probably to a substantial degree. However, it is not a direct or exclusive marker of insulin sensitivity. A significant portion of the insulin-sparing effect after bariatric surgery is driven by weight-loss-independent metabolic, meaning the relationship should be interpreted as multifactorial rather than causal or specific.”

Why HbA1c tells only part of the story

Despite the substantial reduction in insulin requirements, HbA1c remained above recommended targets with an average of 60.0 mmol/mol. Van der Schueren suggests interpreting the findings step by step: surgery induces weight loss, which improves insulin sensitivity, which in turn reduces insulin requirements. HbA1c, however, reflects broader glycaemic control that remains constrained by T1D physiology, glucose variability, and hypoglycaemia risk.

“The discrepancy highlights that insulin dose is a sensitive marker of metabolic improvement, whereas HbA1c is a more conservative and multifactorial outcome in this setting,” Van der Schueren explains.

LeRoux adds that after reaching the weight nadir through bariatric surgery, clinicians should redouble efforts to improve glycaemic control while being cautious about side effects such as hypoglycaemia.

Who benefits most from surgery?

Overall, the study shows that individuals with high baseline HbA1c and high insulin requirements benefit most in terms of glucose control. However, high baseline HbA1c remained predictive of poorer long-term glycaemic control.

“Baseline HbA1c and preoperative metabolic status were strong determinants of postoperative glycaemic outcomes,” says Pazmiño Lucio. “Patients largely carry forward their preoperative glycaemic profile, albeit with moderate improvement after surgery. This makes timing and preoperative optimisation critical.”

As substantial weight loss does not appear to affect glycaemic control in patients with T1D to the same extent as those with T2D, LeRoux suggests “obesity surgery or obesity medicines should be used to reduce the other complications of obesity in patients with T1D and not to focus on glycaemic control as a major determinant of success.”

A valuable option – but not for everyone?

The authors conclude that MBS is a valuable option for people with T1D and very high BMI, while pharmacotherapy may be more appropriate for those with lower BMI, keeping in mind that the study did not compare bariatric surgery with obesity medication in people with T1D.

“Such a study is still urgently awaited in view of the increase in people living with both obesity and T1D,” says Le Roux.

Together, the findings suggest that while bariatric surgery does not cure the underlying disease, it can significantly reduce the metabolic burden of obesity in people with T1D.

Key points:

• Bariatric surgery reduced insulin requirements by 58 % in people with T1D and obesity.
• Participants lost almost one third of their body weight within a year of surgery.
• The metabolic benefits appeared to be driven by reduced obesity-associated insulin resistance.
• HbA1c improved only modestly, suggesting that surgery improves metabolic efficiency more than underlying T1D physiology.

Read the original publication here.

Author: Hanna Gabriel, BA MSc. Any opinions expressed in this article are the responsibility of EASD e-Learning.