Roux-en-Y gastric bypass (RY-GBP) is one of the surgical techniques most widely used for the treatment of obesity. Long series of operated patients published in the literature have demonstrated its safety and efficacy. It consists on the reduction of the size of the stomach and joining it (anastomosis) with the small bowel to reduce the absorption of calories.

Single anastomosis duodenoileal with sleeve gastrectomy is an increasingly used surgical technique that is a simplification of the duodenal switch. It consists on the reduction of the stomach to a tube (sleeve gastrectomy) and an anastomosis between the duodenum and the small bowel. It has been demonstrated as a effective technique and it is supported by the international scientific societies.

There are no data that indicate a superiority of one technique over the other. The objective of this study is to analyze if there are differences between the two techniques in terms of postoperative weight control and gastroesophageal reflux at short, medium and long term.

Obesity is being considered an epidemic of our century. It directly or indirectly contributes as the leading cause of non-traumatic death in the Western population and is progressively reaching developing countries as well. In Spain, recent epidemiological studies estimate that over 15% of the population is at least overweight, and nearly 5% has morbid obesity. The treatment of obesity is multidisciplinary, ranging from lifestyle and dietary changes to surgery. Among all available treatments, the only truly cost-effective option for patients with morbid obesity is bariatric surgery. The beneficial effects go far beyond weight loss, as it has been shown to reduce and improve comorbidities, enhance quality of life, lower cardiovascular risk, and even reduce mortality in individuals affected by obesity.

Duodenal switch (DS) has proven to be the most effective surgical procedure for treating morbid obesity and its comorbidities. However, it currently represents a small percentage of bariatric surgeries performed worldwide, likely due to its technical complexity and the risk of long-term complications. In an effort to simplify the DS technique, in 2007, Drs. Sánchez-Pernaute and Torres introduced the Single Anastomosis Duodeno-Ileal bypass with Sleeve gastrectomy (SADI-S). The omega reconstruction, which avoids the distal ileo-ileal anastomosis, aims to decrease surgical time and reduce postoperative risks. The SADI-S involves a vertical gastrectomy (VG) and a duodeno-ileal anastomosis with preservation of the pylorus, jejunal exclusion, and an original total common channel of 200 cm, standardized later to 250 or 300 cm to minimize the risk of nutritional deficiencies. The SADI-S can be performed as a primary direct surgery, planned in two stages, or as a revisional surgery in case of weight loss failure after VG. Various prospective studies presented on SADI-S show weight loss results and reduction of comorbidities similar to those of large historical series of DS.

The Roux-en-Y gastric bypass (RY-GBP) is currently considered the gold standard of bariatric surgery. It involves creating a small gastric reservoir and a Roux-en-Y gastrojejunostomy.

his is a well-standardized technique with large cohorts of patients followed over the long term, which has demonstrated safety and efficacy in weight control, resolution of metabolic comorbidities, as well as improvement in life expectancy and quality of life. Furthermore, it is the best technique for preventing or treating gastroesophageal reflux (GERD), due to its small gastric reservoir and rapid emptying. However, it has potential specific complications resulting from the non-preservation of the pylorus and mesenteric partitioning: anastomotic ulcer, early or late dumping syndrome, hypoglycemia, and abdominal pain associated with internal hernias. All of these complications are rare but much more frequent after an RY-GBP than after a SADI-S.

Currently, there is only one ongoing study comparing the efficacy and safety of SADI-S with RY-GBP. This is SADISLEEVE (ClinicalTrials.gov ID NCT03610256), a French multicenter randomized study that has several methodological limitations in its design: it includes both patients undergoing primary and revisional surgery, without BMI restrictions and with varying lengths of limbs.

The present prospective randomized study aims to compare SADI-S with RY-GBP. It includes patients with a BMI between 40 and 50 kg/m² for whom gastric bypass would be indicated at the participating centers. Patients who do not meet the requirements for bariatric surgery, as well as those with contraindications for hypoabsorptive or mixed surgery, are excluded.

The project has two objectives: a) efficacy: to compare the percentage of weight lost at 2 and 5 years after the two surgical procedures; b) safety: to assess the percentage of serious complications at 2 and 5 years. Routine follow-up controls from both Endocrinology and Dietetics, as well as General Surgery, will be used for both.

The most relevant secondary objective is to compare quality of life, for which SF-12 questionnaires will be systematically administered, along with the most likely factors affecting it: resolution of comorbidities, symptoms of GERD, abdominal pain, dumping syndrome, hypoglycemia, diarrhea, and need for supplementation. Gastroscopy and esophageal pH-impedance measurement will also be performed before the operation and at 2 and 5 years post-surgery.

Other secondary objectives include comparing short-term complications and studying nutritional and metabolic deficits of both procedures in the medium and long term. For the study of morbidity and mortality, the electronic medical records of the patients will be used, classifying immediate postoperative events (up to 30 days post-intervention) according to the Clavien-Dindo classification. The analysis of comorbidity evolution will involve monitoring factors related to metabolic risk in these patients before the intervention and annually thereafter, utilizing the infrastructure of the patient follow-up protocol. Finally, the analysis of metabolic and nutritional deficits will be conducted through comparative analysis of the annual analytical data systematically collected during the follow-up of the intervened patients.

Main Hypothesis: The Single Anastomosis Duodeno-Ileal bypass (SADI-S) is associated with greater efficacy (higher percentage of weight loss) and similar safety (equal or lower percentage of serious complications) at two and five years post-surgery compared to gastric bypass (RY-GBP) in patients with grade III morbid obesity (BMI between 40 and 50 kg/m²).

Secondary Hypotheses:

1. SADI-S is associated with lower incidence of digestive symptoms: dumping syndrome, hypoglycemia, and abdominal pain.
2. SADI-S is associated with better quality of life than RY-GBP.
3. RY-GBP is associated with a lower risk of GERD and a higher risk of anastomotic ulcer.
4. The complication rates of both techniques in the immediate postoperative period (up to 30 days post-intervention) are similar.
5. SADI-S achieves higher rates of resolution of metabolic syndrome comorbidities: type 2 diabetes mellitus (T2DM), hypertension (HT), dyslipidemia (DL), and sleep apnea (SA).
6. Patients undergoing SADI-S and RY-GBP require similar supplementation to compensate for nutritional deficits in the short, medium, and long term.
7. Baseline eating habits are related to weight loss at 2 and 5 years within each of the two patient groups.
8. Differences in acid and bile reflux occur between the two techniques, which can be objectively measured with functional tests such as pH-metry, impedance measurement, and bilitec.

Inclusion Criteria:

• BMI 40 - 50 Kg/m2
• Candidates to mixed bariatric surgery

Exclusion Criteria:

• < 18 years.
• > 60 years.
• BMI < 40 Kg/m2
• BMI > 50 Kg/m2.
• Non-candidates to mixed bariatric surgery.

IPD will be shared upon request to the principal investigator.

Beginning 1 year after publication with no end date.

The requests for IPD sharing will be reviewed by the IP and a committee of the IPs from the different centers. Access will be granted for systematic reviews and metaanalysis.