Type 2 Diabetes and Metabolic Surgery: When Bariatric Surgery Can Help

"Metabolic surgery" is the term used when bariatric surgery is indicated partly for its effect on metabolic disease, above all type 2 diabetes. The most common operations are sleeve gastrectomy (gastric sleeve) and Roux-en-Y gastric bypass.

The effect on blood sugar does not come from weight loss alone. Surgery also changes how food travels through the digestive tract and the hormonal signals between the gut, pancreas and brain, which influences appetite and how the body handles glucose. This is why, in some patients, glucose values improve within the first weeks, before major weight loss.

In 2022 the international bariatric surgery societies ASMBS and IFSO updated their indications. In short:

• surgery is recommended from a BMI ≥ 35 kg/m², whether or not other conditions are present;
• surgery may be considered at a BMI of 30–34.9 kg/m² in people with metabolic disease such as type 2 diabetes;
• thresholds are lower for patients of Asian origin, because metabolic risk appears at lower BMI values.

The joint statement of international diabetes organizations (DSS-II, 2016) placed metabolic surgery in the type 2 diabetes treatment algorithm: recommended at BMI ≥ 40 kg/m² and at BMI 35–39.9 kg/m² when blood sugar is inadequately controlled by lifestyle and optimal medical therapy, and to be considered at BMI 30–34.9 kg/m² when blood sugar remains uncontrolled despite optimal oral or injectable treatment.

You can check your body mass index with our BMI calculator. BMI is only the starting point; the decision is made after a full medical evaluation.

STAMPEDE (Schauer et al., NEJM 2017) randomized 150 patients with type 2 diabetes and a BMI of 27 to 43 to intensive medical therapy alone or medical therapy plus gastric bypass or sleeve gastrectomy. At 5 years, an HbA1c of 6.0% or less (with or without medication) was reached by 5% of patients on medical therapy alone, 29% after bypass and 23% after sleeve. The mean reduction in HbA1c was 2.1% after surgery versus 0.3% with medical therapy.

The Mingrone trial (Lancet 2021) followed 60 patients with diabetes of more than 5 years' duration and a BMI ≥ 35 for 10 years. Ten-year remission was 5.5% with medical therapy, 25.0% after gastric bypass and 50.0% after biliopancreatic diversion. Of the patients in remission at 2 years, 58.8% later had a relapse of hyperglycaemia, yet all kept adequate glycaemic control at 10 years (mean HbA1c 6.7%). Operated patients had fewer diabetes-related complications.

The authors concluded that metabolic surgery was more effective than conventional medical therapy for long-term diabetes control — but full remission was not the rule for everyone.

Surgery is not a promise of a cure. A few things to know before deciding:

• Remission does not occur in every patient, and when it does, diabetes can return over time, as the trials above showed.
• The stage of diabetes matters. The IMS score uses four factors: diabetes duration, number of medications, insulin use and glycaemic control. In the merged SLEEVEPASS and SM-BOSS data, 5-year remission was 87.5% (sleeve) and 85.7% (bypass) in the mild stage, 42.9% and 45.2% in the moderate stage, and 18.2% and 0% in the severe stage.
• C-peptide helps the doctor estimate how much insulin the pancreas still produces. A low reserve may mean medication will still be needed after surgery.
• Even when diabetes does not go into remission, many patients need less medication — but this is assessed individually.

No single procedure suits everyone. In the merged data of the SLEEVEPASS and SM-BOSS randomized trials (Wölnerhanssen et al., 2021), there was no difference in type 2 diabetes remission between sleeve and bypass at 5 years. Bypass led to somewhat greater weight loss (62.7% versus 55.5% excess BMI loss) and better remission of hypertension, but the complication rate was higher after bypass (37.2% versus 22.5%).

In practice, the bariatric team considers the stage of your diabetes, gastro-oesophageal reflux, other conditions, the medicines you take and your own preferences. You can read more on the gastric sleeve and gastric bypass pages.

For a free, confidential online pre-assessment, it helps to send:

• a recent HbA1c and fasting glucose;
• C-peptide (if measured; if not, the team can tell you whether it is needed);
• a complete medication list with doses: tablets, non-insulin injections, insulin (type and units per day);
• how long you have had diabetes and any known complications (kidneys, eyes, nerves, heart);
• your weight, height and other conditions (high blood pressure, sleep apnoea, reflux).

Before surgery in Istanbul, blood tests, specialist reviews and usually an upper endoscopy are carried out according to the confirmed medical plan.

Diabetes treatment often changes within the first days after surgery, because food intake falls sharply. Doses are adjusted only together with your doctor — do not stop or reduce insulin or other medicines on your own. You will receive clear instructions for monitoring your blood sugar at home, and working with your diabetes doctor at home remains important in the long term.

For a sleeve, the typical plan is about 2 hospital nights and 3 hotel nights; for a bypass, 4 hospital nights and about 5 hotel nights. Prices start from €2,500 for sleeve and from €3,500 for bypass, including complications insurance with 6-month coverage through Sompo Sigorta; the final price is confirmed in writing after a full medical evaluation. For 12 months you receive online nutrition and follow-up support, and your coordinator answers on WhatsApp. To start an assessment, contact us here.

• Eisenberg D, Shikora SA, Aarts E, et al. 2022 American Society for Metabolic and Bariatric Surgery (ASMBS) and International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO): Indications for Metabolic and Bariatric Surgery. Surg Obes Relat Dis. 2022;18(12):1345-1356.
• Rubino F, Nathan DM, Eckel RH, et al. Metabolic Surgery in the Treatment Algorithm for Type 2 Diabetes: A Joint Statement by International Diabetes Organizations. Diabetes Care. 2016;39(6):861-877.
• Schauer PR, Bhatt DL, Kirwan JP, et al. Bariatric Surgery versus Intensive Medical Therapy for Diabetes - 5-Year Outcomes. N Engl J Med. 2017;376(7):641-651.
• Mingrone G, Panunzi S, De Gaetano A, et al. Metabolic surgery versus conventional medical therapy in patients with type 2 diabetes: 10-year follow-up of an open-label, single-centre, randomised controlled trial. Lancet. 2021;397(10271):293-304.
• Wölnerhanssen BK, Peterli R, Hurme S, et al. Laparoscopic Roux-en-Y gastric bypass versus laparoscopic sleeve gastrectomy: 5-year outcomes of merged data from two randomized clinical trials (SLEEVEPASS and SM-BOSS). Br J Surg. 2021;108(1):49-57.
• Saarinen I, Grönroos S, Hurme S, et al. Validation of the individualized metabolic surgery score for bariatric procedure selection in the merged data of two randomized clinical trials (SLEEVEPASS and SM-BOSS). Surg Obes Relat Dis. 2023;19(5):522-529.