What is (SASI) Bipartition Surgery?

Bariatric surgery is an umbrella term for operations designed to help people with severe obesity achieve lasting weight loss, improve metabolic health, and address obesity-related concurrent conditions such as diabetes and hypertension. In general, these surgeries can be categorized as:

• Restrictive procedures like sleeve gastrectomy (LSG), which reduce stomach size to limit food intake and lower hunger hormones.
• Malabsorptive procedures like duodenal switch (DS) or Roux-en-Y gastric bypass (RYGB), which reroute portions of the intestines to reduce calorie absorption.
• Hybrid or metabolic procedures such as single anastomosis gastric bypass (OAGB/BAGUA) or SADI-S, which combine restriction with targeted intestinal modifications to enhance metabolic benefits.

Each approach balances weight loss effectiveness, comorbidity improvement, and risk of nutrient deficiencies differently, which is why choosing the right procedure depends on a patient’s goals, health profile, and prior treatments.

A Newer Surgical Option

Bipartition surgery is also referred to as transit bipartition (TB) or Single Anastomosis Sleeve Ileal Bypass (SASI). At its core, both TB and SASI involve two main components:

• Sleeve gastrectomy (restriction): Approximately 80% of the stomach is removed, leaving a narrow “sleeve” that limits food intake and reduces the hunger hormone ghrelin.
• Dual intestinal pathway (transit bipartition): A second route is created from the stomach to the ileum, so food partially bypasses the proximal small intestine while still traveling through the normal route. This stimulates hormones in the distal gut that promote satiety and regulate metabolism, while preserving nutrient absorption.

TB and SASI are closely related but not identical; the difference is in how the intestinal connection is configured:

• TB is the original procedure concept, which can involve multiple intestinal routing configurations and sometimes a Roux-en-Y reconstruction.
• SASI bypass uses a single gastroileal anastomosis (called an omega loop), making the procedure technically simpler and easier to reproduce while still achieving the same metabolic and weight-loss benefits.

All SASI bypasses are TBs, but not all TBs are SASI; the SASI is just a modern, streamlined version of TB.

Because it incorporates a sleeve gastrectomy, bipartition can be performed as a standalone procedure in patients seeking primary metabolic surgery. It can also be combined with other procedures in certain situations, particularly in revisional bariatric surgery. For example:

• Patients who initially had a sleeve gastrectomy but regained weight or have persistent metabolic issues may undergo bipartition as a second-stage procedure.
• Compared with more malabsorptive revisions like duodenal switch, the lower risk of nutrient deficiencies makes it an attractive option for revisional interventions.

Bipartition is a desirable addition to the spectrum of bariatric surgeries; its design reflects an evolving understanding of how the stomach, intestines, and associated hormones work together to influence appetite, metabolism, and long-term weight control.

What Does it Accomplish?

Stomach shrinking tends to come to mind when discussing weight loss surgery, but it actually targets the metabolic and hormonal aspects of obesity, as well as physiological changes, for a multi-pronged approach.

By combining restriction and pathway techniques, bipartition surgery reduces caloric intake while stimulating hormones that signal satiety (anorexigenic hormones), including peptide YY and GLP-1. One study showed substantial weight reduction when used as a primary bariatric procedure, with some patients losing up to 86% of excess weight. If someone’s ideal body weight is 150 pounds but they weigh 250 pounds before surgery, the “excess weight” is 100 pounds. Losing 86% of that excess weight would result in roughly 86 pounds lost, bringing their post-surgery weight to around 164 pounds. If that isn’t enough, most research participants also reported high levels of satisfaction, reflecting improvements not only in weight but also in symptoms like acid reflux.¹

Additionally, obesity-related conditions, including type 2 diabetes and high blood pressure, tended to improve following the procedure.1 By diverting a portion of food to the distal ileum, the procedure increases hormonal signaling that improves insulin sensitivity, supports glucose control, and can even lead to diabetes remission in some patients.

In another research group, participants who underwent TB/SASI as a first-line intervention showed as much as 27% total weight loss at one year post-surgery.¹ To give this context, if someone weighs 250 pounds before surgery, they could experience roughly 67 pounds of weight loss, dropping their weight to approximately 182-183 pounds.

Unlike malabsorptive procedures like duodenal switch, nutrient absorption is largely preserved with TB/SASI, reducing the likelihood of vitamin or mineral deficiencies. Combined with its effectiveness in weight reduction and metabolic improvement, bipartition surgery is a strong contender for the revisional setting as well.

Who Is It For?

Like other metabolic surgeries, candidacy is typically based on body mass index (BMI) and related health conditions. Most patients qualify with a BMI of 35 or higher accompanied by comorbidities such as type 2 diabetes, hypertension, or sleep apnea, though some centers consider those with a BMI as low as 30 if metabolic disease is also present.

The best candidates are those prepared to make long-term lifestyle changes in diet, physical activity, and follow-up care. As with any bariatric procedure, sustained success depends on a partnership between the patient and their surgical team. Bipartition surgery can do incredible things: recalibrate hormones, reduce hunger, restore insulin sensitivity. But it’s your daily choices that make those changes permanent.

Even with incredible practitioners on your side, you’re the author of what happens next. Some patients think they need a miracle when all they really need is a method. If you’re ready to make a decision that changes your body and your trajectory, the Gastric Sleeve Center is where new chapters begin. We’ll help you understand your options, your metabolism, and your next best move.

¹Reiser, M., Christogianni, V., Nehls, F., Dukovska, R., de la Cruz, M., & Büsing, M. (2021). Short-term Results of Transit Bipartition to Promote Weight Loss After Laparoscopic Sleeve Gastrectomy. Annals of surgery open : perspectives of surgical history, education, and clinical approaches, 2(4), e102. https://doi.org/10.1097/AS9.0000000000000102.