The Single Anastomosis Duodeno–Ileal bypass/switch, commonly referred to as SADI or SADI-S, is a modern bariatric surgery. It is considered a modification of the traditional Duodenal Switch procedure, simplifying the operation while maintaining results. SADI combines two methods of achieving weight loss and metabolic improvement: restricting the amount of food a person can consume and limiting the body’s ability to absorb calories and nutrients. This dual-action approach is effective for patients with high body mass indexes (BMI) and complex health conditions like Type 2 diabetes.
How the SADI Procedure Alters Digestion
The SADI procedure involves two major anatomical changes. The first component is a vertical sleeve gastrectomy (VSG), where approximately 80% of the stomach is removed, leaving a narrow, tube-shaped pouch. This reduction restricts the amount of food that can be eaten, contributing to an immediate feeling of fullness. Removing the outer portion of the stomach also reduces the production of ghrelin, the “hunger hormone,” which helps diminish appetite.
The second component is the intestinal bypass, which is the primary driver of the surgery’s metabolic effects. The surgeon divides the first part of the small intestine, the duodenum, just past the stomach’s natural outlet, the pylorus. The divided end of the duodenum is then connected to a lower segment of the small intestine, the ileum, bypassing a significant portion of the digestive tract. This single connection, or anastomosis, is what gives the procedure its name.
This rerouting ensures that undigested food and digestive juices, including bile and pancreatic enzymes, only mix in the final section of the small intestine, known as the common channel. Shortening the length of the intestine available for nutrient absorption induces malabsorption. This means fewer calories, fats, and sugars are absorbed into the body. The rapid delivery of food to the lower intestine also triggers favorable changes in gut hormone signaling, which improves blood sugar control and metabolic health.
Criteria for Patient Eligibility
The SADI procedure is reserved for individuals with severe or “morbid” obesity who have not achieved adequate results through non-surgical weight loss methods. Guidelines recommend SADI for patients with a BMI of 50 or higher, or a BMI of 40 or higher with significant obesity-related health issues. Patients with a BMI between 35 and 39.9 who have serious comorbidities like Type 2 diabetes, severe hypertension, or obstructive sleep apnea may also be considered.
SADI is also an option for patients who previously underwent a sleeve gastrectomy but experienced insufficient weight loss or significant weight regain. This revision converts the sleeve into a SADI by adding the malabsorptive intestinal component. All candidates must commit to lifelong medical follow-up, including adherence to specific dietary and nutritional supplement regimens due to the surgery’s malabsorptive nature.
Advantages Over Traditional Weight Loss Surgeries
SADI offers advantages compared to procedures like the Roux-en-Y Gastric Bypass (RNY) and the standard Vertical Sleeve Gastrectomy (VSG). SADI provides a greater degree of weight loss and more significant improvement in metabolic diseases, such as Type 2 diabetes, especially for patients with a high starting BMI. Studies show that SADI can result in an average excess weight loss of 80% or more, often surpassing the outcomes of VSG and RNY.
A primary benefit of SADI is the preservation of the pylorus, the natural valve regulating stomach emptying. Maintaining this valve helps prevent rapid gastric emptying, which reduces the risk of developing dumping syndrome, a common complication after RNY gastric bypass. Pylorus preservation also allows for easier endoscopic access to the bile ducts for future diagnostic or therapeutic procedures.
The SADI procedure requires only a single surgical connection, or anastomosis, to reroute the intestine, unlike the RNY procedure, which requires two. This single-connection design makes the SADI operation simpler and faster to perform. The simpler anatomical rearrangement also results in a lower risk of internal hernia formation, a complication associated with the two-anastomosis RNY bypass.
Long-Term Nutritional Requirements and Specific Risks
Because the SADI procedure intentionally reduces nutrient absorption, it requires lifelong monitoring and consistent supplementation to prevent deficiencies. The altered anatomy reduces the absorption of fat-soluble vitamins (A, D, E, and K), which are absorbed with dietary fat.
Patients are also at a higher risk for deficiencies in Vitamin B12, iron, and calcium, requiring high-potency multivitamins and specific supplements. Non-adherence to this regimen can lead to severe health issues, including anemia, bone density loss, and protein-calorie malnutrition. Lifelong protein intake goals, typically 80 to 100 grams per day, are set to maintain muscle mass and prevent protein deficiency.
A specific risk of the SADI procedure is the potential for chronic diarrhea or steatorrhea (excess fat in the stool). This is a direct consequence of the reduced length of the common channel where fats are absorbed. It is often managed through dietary modifications, such as limiting high-fat foods. Although SADI mitigates the risks of the older Duodenal Switch, severe malabsorption may require an additional surgical revision to lengthen the common channel.