Serious complications after the newer SADI-S operation ran 5.2% in a surgeon's first 20 cases and 0.9% after

Surgeons in Michigan have published a multi-hospital safety review of SADI-S, one of the newest weight-loss operations, and the numbers point at something patients can act on. Across 330 operations there were no deaths and a 2.7 percent rate of serious complications. But serious complications were far more common while a surgeon was still learning the procedure.

The study appeared in Surgery for Obesity and Related Diseases, the journal of the American Society for Metabolic and Bariatric Surgery. It was posted online on August 10, 2026 and indexed by the National Library of Medicine on September 4, 2026.

A newer operation that makes one intestinal connection instead of two

SADI-S stands for single anastomosis duodeno-ileal bypass with sleeve gastrectomy. An anastomosis is a surgical join between two sections of intestine. The name says the operation makes only one of them.

The surgery begins the same way as a sleeve gastrectomy, with most of the stomach removed to leave a narrow tube. The surgeon then divides the small intestine just past the stomach and connects a lower loop of intestine directly to it. Food travels a shorter route through the gut, and the body absorbs fewer calories and fewer nutrients.

ASMBS describes SADI-S as the most recent operation it has endorsed, and lists among its drawbacks that it is a newer operation with only short-term outcome data. That is the gap this study set out to narrow.

330 operations across nine hospitals, no deaths, 2.7 percent serious complications

The researchers used the Michigan Bariatric Surgery Collaborative, a registry that has collected data from bariatric programs across the state since 2005. A registry records every operation a participating hospital performs, rather than only the cases a surgeon chooses to write up. That makes disappointing results harder to leave out.

The collaborative spans 41 hospitals. Between 2016 and 2025, 13 surgeons at nine of those hospitals performed 330 primary SADI-S operations. Serious complications occurred in 2.7 percent of them. The researchers counted a complication as serious if it involved a major heart or lung event, a leak at the intestinal join, kidney failure, a surgical site infection, a blood clot in a vein, or a return to the operating room.

No patient died. Complication rates stayed at or below 2.7 percent even in 2022, when the number of cases jumped.

Serious complications ran 5.2 percent in a surgeon's first 20 cases and 0.9 percent after

The learning curve was the sharpest finding. Among the surgeons in this group, serious complications occurred in 5.2 percent of a surgeon's first 20 SADI-S operations, and in 0.9 percent of the operations that followed.

The authors reported a P value of .018 for that difference. A P value that small means a gap this large would be unlikely to show up by chance alone if experience made no difference. It does not prove experience was the cause, and it does not tell you how large the true difference is.

The researchers also checked whether any individual surgeon stood out as unusually risky, using two methods. A funnel plot compares each surgeon's complication rate against how many cases that surgeon performed, since surgeons with few cases naturally show more variation. A cumulative sum analysis, often shortened to CUSUM, tracks results case by case to flag a surgeon whose outcomes drift worse over time. Neither method flagged anyone among the six surgeons who had performed more than 15 cases.

One state, 330 cases, and no weight or nutrition data

This was an observational study, not a randomized trial, and its limits are real.

330 operations is a small number for measuring rare events. No deaths in 330 cases is reassuring, but it does not mean the risk is zero. Statisticians use a rule of thumb that when no events occur in a study, the true rate could still be as high as roughly three divided by the number of patients. Here that works out to about 1 in 110.

The authors framed their conclusion around experienced mid-career bariatric surgeons. The study says little about what happens when a surgeon newer to bariatric surgery takes up SADI-S, or at a hospital performing a handful of these cases a year. The surgeon-level monitoring covered six of the 13 surgeons, because the other seven had not performed enough cases to analyze that way.

The results cover short-term surgical complications only. They say nothing about how much weight patients lost, whether diabetes improved, or whether patients developed the vitamin and mineral deficiencies that operations rerouting the intestine are known to cause. Those outcomes take years to measure, and they are a large part of what decides whether an operation was the right choice.

All the data came from one state. Michigan hospitals in this collaborative report into a shared quality program and meet regularly to compare results, which is not how every bariatric program in the country operates.

The registry is funded by Blue Cross Blue Shield of Michigan and Blue Care Network through the insurer's Value Partnerships Program, and four of the authors reported honoraria or salary support from Blue Cross Blue Shield of Michigan for their roles leading the collaborative. No drug or device maker was reported as funding the work.

Anyone weighing SADI-S against a sleeve gastrectomy, a gastric bypass, or a traditional duodenal switch should work through their own risks with their surgical team. How many of these specific operations the surgeon has performed is a fair question to ask.