Weight Loss, Comorbidity, and Complications After Single-anastomosis Sleeve Ileal Bypass (SASI): A Systematic Review and Meta-analysis

Abstract

Single anastomosis sleeve ileal (SASI) bypass combines sleeve gastrectomy with intestinal bipartition to promote weight loss and metabolic improvement. We conducted a systematic review and meta-analysis comparing SASI with sleeve gastrectomy (1 RCT and 4 non-randomized comparative studies (NRCTs)), one-anastomosis gastric bypass (2 RCTs, 4 NRCTs), and Roux-en-Y gastric bypass (2 NRCTs), regarding weight loss, metabolic and nutritional outcomes, and adverse effects. Certainty of evidence was assessed with GRADE for 1-year outcomes. Twenty-six studies (1603 patients) were included, mostly reporting 12-month results. Pooled single-arm analysis from 11 studies showed mean total weight loss of 35.9 kg (95% CI 33.3–38.5). The certainty of evidence ranged from low to very low, limiting confidence in the results and emphasizing the need for high-quality RCTs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11695-026-08793-0.

Key Points

We are very uncertain whether SASI differs from SG, OAGB, or RYGB for weight loss at 12 months (very low-certainty evidence).

SASI may result in better outcomes for diabetes remission compared to SG (low-certainty evidence), but we are very uncertain about comparisons with OAGB and RYGB (very low-certainty evidence).

The evidence base consists of few, small studies with substantial methodological limitations, and data beyond 12 months are scarce.

High-quality, adequately powered RCTs with standardized techniques and longer follow-up are needed to establish the comparative effectiveness of SASI.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11695-026-08793-0.

Introduction

The rising prevalence of obesity and related metabolic disorders is a major contributor to the global burden of disease [1]. While effective pharmacologic treatments for obesity are emerging, their long-term efficacy and safety are not established. Metabolic bariatric surgery (MBS) is the most effective intervention for achieving substantial and sustained weight loss and for improving metabolic disease [2]. Currently, the most applied surgical techniques include sleeve gastrectomy (SG), Roux-en-Y gastric bypass (RYGB), and one anastomosis gastric bypass (OAGB), each offering distinct advantages while presenting specific risks of complications and adverse effects [3]. Procedures with a large foregut bypass, such as biliopancreatic diversion with duodenal switch, are highly effective in reducing body weight, but are associated with a substantial risk of nutritional deficiencies [4].

Efforts to develop new, safe, and effective surgical techniques are ongoing. Dr. Sergio Santoro introduced SG with transit bipartition, incorporating a large foregut bypass while preserving partial foregut continuity. In theory, this reduces the risk of malabsorption while maintaining hindgut stimulation [5]. Later, Mui et al. and Mahdy et al. modified the surgical approach to a single anastomosis technique presented as loop-bipartition or single-anastomosis sleeve ileal bypass (SASI) [6, 7]. The latest update from the International Federation for the Surgery of Obesity and Metabolic Disorders classifies these operations as investigational MBS procedures [8].

A possible advantage of the bipartition technique is that no segment of the gastrointestinal tract is excluded, preserving endoscopic access to the stomach and biliary system. Additionally, reversal of SASI to SG is relatively straightforward in cases of adverse events, such as nutritional complications [6, 9].

Initial studies suggest that SASI enables substantial weight loss and metabolic improvements, with outcomes comparable to or exceeding those of established bariatric procedures. However, concerns persist about the risk of protein-calorie malnutrition and long-term effects, warranting further evaluation [9, 10].

Although previous systematic reviews comparing SASI with established methods exist, these studies did not include assessments of evidence quality, which limits the ability to evaluate confidence in the results [9–12]. Additionally, new studies have been published after the completion of previous systematic reviews (the most recent search was up to December 2023). The primary aim of this systematic review is therefore to update the evidence base on the relative effect of SASI to other bariatric procedures regarding weight reduction, remission of type 2 diabetes (T2DM), remission of dyslipidemia, nutritional status, and complications; and assess the certainty of evidence using the GRADE approach. SASI is a relatively newly developed surgical technique and a limited number of studies are expected to be available for analysis.

Methods

Eligibility Criteria

Studies were included if they met the following criteria: (1) Adults of both sexes with obesity grade II with serious obesity-related health problem or obesity grade III; (2) Surgical intervention of SASI with a common intestinal channel of 250 cm to 350 cm; (3) Randomized controlled trials (RCTs) or non-randomized comparative trials (NRCTs) evaluating SASI with other bariatric procedures or pharmacological treatment, and single-arm cohort studies of ≥ 20 patients; (4) Reported outcomes on weight loss, and/or improvement in T2DM, dyslipidemia, surgical complications, or nutritional changes represented by changes in levels of albumin, hemoglobin (Hb), ferritin, vitamin D and/or vitamin B12; (5) A minimum follow-up period of 1-year; (6) Published in English, German, French, Norwegian, Swedish or Danish.

Exclusion criteria were studies with overlapping populations (largest cohort study was included), studies including SASI as a revisional bariatric procedure, studies with < 1-year follow-up, studies using different surgical techniques than described above, case reports or patient series with < 20 participants, animal studies, and abstracts, correspondence, editorials and reviews. This review adhered to the PRISMA guidelines [13]. The study adhered to the protocol registered in PROSPERO (ID CRD42024593532): https://www.crd.york.ac.uk/PROSPERO/view/CRD42024593532.

Search Strategy

Papers published from inception until January 17, 2025 were searched in Ovid Medline, Embase, and Cochrane Central Register of Controlled Trials using search terms expressing “single-anastomosis sleeve ileal bypass”. There were no date or language restrictions. A detailed search strategy is provided in Appendix A. Reference lists of publications identified through the above strategy were examined for other relevant studies.

Study Selection

We used the Covidence systematic review software for study selection [14]. Duplicates were removed before one reviewer performed primary screening of titles and abstracts. Uncertainties were resolved with a second reviewer. Two reviewers performed full-text screening of the remaining articles independently, with disagreements resolved by a third reviewer.

Data Extraction

One review author (HMH) extracted data from the included studies using a piloted data extraction form. We retrieved demographic and clinical data including technical details of the procedure and the following outcomes: (1) Body Mass Index (BMI) preoperatively and at annual follow-ups; (2) % total weight loss (%TWL) or alternatively % excessive weight loss (%EWL) where %TWL was not reported; (3) Prevalence and remission of T2DM; (4) Remission of dyslipidemia; (5) Early (< 30 days), and long-term complication rates; (6) Rates of reoperations during the observation period; (7) Changes in levels of albumin, Hb, ferritin, vitamin D and vitamin B12 from baseline to 1 year postoperatively or last reported follow-up. These parameters were chosen as measures of nutritional outcomes as these were most reported across the studies.

Data Synthesis

The primary aim of this review was to evaluate the effect of SASI compared to established MBS procedures. Because only a limited number of comparative studies were available, we also performed single-arm analyses by pooling data from all SASI patients, irrespective of comparison group or study design, to provide supplementary information about the absolute effectiveness of this procedure.

Analyses were based on data collected 1 year after surgery, except for long-term morbidity and mortality, for which we included all available follow-up data as reported in the original studies. Missing data was not imputed. Median follow-up across studies was 12 months. Data were too sparse to support formal analyses of longer-term outcomes; however, weight-loss outcomes beyond 1 year are summarized descriptively in a separate table. Data on long-term comorbidities were generally not reported with sufficient clarity to allow extraction.

Comparative Analyses

For dichotomous data, we extracted the number of participants in each treatment arm who had the outcome of interest, and the number of participants assessed, to estimate the risk ratio (RR). For continuous data, we calculated the mean difference (MD) with standard deviation (SD). Random-effects meta-analyses were performed where applicable, using Cochrane Review Manager (RevMan), version 9.19.0 (The Cochrane Collaboration) [15]. Definitions and reporting of complications varied substantially across studies, and precluded meta-analysis, and is therefore presented narratively. Data is otherwise presented in forest plots, text and tables. Analyses and results were performed and presented separately for RCTs and NRCTs without any pooling of these results.

Pooled Analyses

Single-arm analyses were performed with Stata Statistical Software: Release 18 (StataCorp LLC, College Station, TX, USA) [16] by pooling data from all SASI patients, irrespective of comparison group or study design, for %TWL, T2DM and dyslipidemia. Complication rates are reported descriptively due to the same limitations as for the comparative studies. The results are presented separately from the comparative analyses, and should be interpreted with caution in light of heterogeneity in study design, patient populations, and risk of bias. The comparative studies are presented first to highlight the relative effectiveness of SASI to other established procedures.

Outcome Definitions and Units

The definition of diabetes remission varied across studies, Table S1, and we included all definitions in our analyses. Definition of remission of dyslipidemia was often not stated or defined as normal lipid values without use of lipid lowering medication. We report rates of dyslipidemia remission as stated in the original articles. Units are primarily extracted as reported. For vitamin B12, the standardized mean difference (std.MD) is reported in meta-analyses due to variations in units reported. In tables summarizing nutritional results, measurements are converted to SI units to help comparability. When units were not explicitly stated in the original publication, this is indicated in the results section and supplementary tables by “not reported”, and no conversion was attempted. Outcomes not presented with uncertainty measures could not be included in the meta-analysis.

Terminology

A 2025 consensus meeting in Strasbourg (unpublished) recommended “one-anastomosis transit bipartition” as the preferred term for this operation, without distinguishing between ileal or jejunal anastomoses. In this review, we use SASI as the main acronym, as our inclusion criteria are limited to ileal anastomoses and most included studies used this terminology.

Quality Assessment

The risk of bias was assessed using the Cochranes ROB2 tool for RCTs [17]; The Newcastle-Ottawa Scale for comparative NRCTs [18]; The JBI appraisal tool for case series studies [19]. Two authors independently assessed the studies with disagreements resolved through discussion with a third author. Details are provided in Appendix B.

Certainty of Evidence

For the comparative analyses of outcomes at 1 year, we applied the GRADE approach for grading the certainty of evidence for %EWL/%TWL, remission of T2DM and dyslipidemia, and nutritional parameters in the RCTs and NRCTs; and used the GRADEpro software to construct a summary of findings tables, Appendix C [20, 21].

Results

Study Selection

The literature search identified 209 studies. After removing duplicates, 145 studies were screened, and 49 were selected for full-text review, Fig. 1. The final review comprised 26 studies including 1603 patients with completed 12 months follow-up: 3 RCTs, 7 NRCTs, and 16 single-arm cohort studies. One RCT and 4 NRCTs compared SASI to SG, 2 RCTs and 4 NRCTs compared SASI to OAGB, and 2 NRCTs compared SASI to RYGB, Table 1. There were no articles comparing SASI to medical treatment.

Fig. 1.

PRISMA flow chart of study selection

Table 1.

Study characteristics

Author, year (reference)	Country	Study design	Comparator	Sample size (n)	Follow-up (months)	Female (%)	Age (mean years)
Abdalaziz, 2022 [36]	Macedonia	SAOCS	none	47	12	70.2	38.5
Abdelrahman, 2024 [37]	Egypt	SAOCS	none	50	12	70.0	41.6
Abouzeid, 2019 [38]	Egypt	SAOCS	none	20	12	80.0	40.6
Aghajanai, 2023 [39]	Norway	SAOCS	none	229	Up to 48	77.9	41.0
Barakat, 2023 [40]	Egypt	SAOCS	none	75	Up to 24	76.0	36.9
Demir, 2023 [29]	Turkey	NRCT	LSG-TB (15) + OAGB (50)	32	12	53.1	48.8
Erol, 2024 [30]	Turkey	NRCT	RYGB (68)	51	24	62.7	42.5
Hosseini, 2022 [41]	Iran	SAOCS	none	116	Up to 36	84.5	42.2
Kamal, 2023 [32]	Egypt	SAOCS	none	30	12	50.0	44.1
Kermansaravi, 2020 [42]	Iran	SAOCS	none	24	12	79.2	41.8
Khalaf, 2021 [43]	Egypt	SAOCS	none	322	Up to 24	61.5	37.4
Khalil, 2019 [22]	Egypt	RCT	SG (25)	26	12	73.1	38.6
Mahdy, 2016 [7]	UAE	SAOCS	none	50	12	66.0	40.5
Mahdy, 2021 (a) [25]	UAE	NRCT	SG (99) + OAGB (91)	74	12	70.3	39.9
Mahdy, 2021 (b) [31]	UAE	NRCT	RYGB (46)	46	12	50.0	38.4
Mohamed, 2020 [28]	Bahrain	NRCT	SG (104) + OAGB (39)	34	12	NR	NR
Moustafa, 2020 [24]	Egypt	RCT	OAGB (30)	30	12	90.0	40.3
Nawar, 2024 [23]	Egypt	RCT	OAGB (31)	31	12	74.0	36.2
Parkitna, 2024 [44]	Poland	SAOCS	none	40	26	90.0	42.0
Ribeiro, 2023 [45]	Portugal	SAOCS	none	41	Up to 60	75.0	45.5
Romero, 2021 [46]	Mexico	SAOCS	none	43	12	62.6	40.5
Salama, 2017 [47]	Egypt	SAOCS	none	45	12	75.6	31.2
Vennapusa, 2017 [48]	India	SAOCS	none	56	12	41.6	40.7
Wafa, 2024 [33]	Libya	SAOCS	none	30	12	93.3	37.4
Yildirak, 2023 [26]	Turkey	NRCT	SG (30)	31	12	80.7	49.3
Yu, 2024 [27]	China	NRCT	SG (263) + OAGB (30)	30	12	43.3	37.6

UAE United Arabic Emirates, RCT Randomized controlled trial, NRCT non-randomized comparative study, SAOCS single-arm cohort study, SASI single-anastomosis sleeve ileal bypass, SG sleeve gastrectomy, OAGB one anastomosis gastric bypass, LSG-TB laparoscopic sleeve gastrectomy with transit bipartition, RYGB Roux-en-Y gastric bypass, NR not reported, NS Not specified

Risk of Bias

Details are presented in Appendix B. ROB2 evaluation indicated “some concerns” for two RCTs [22, 23], and “high risk” for one RCT [24]. We considered the NRCTs evaluated, using the Newcastle Ottawa scale, to be of poor quality, mostly due to inadequate control for important confounders or non-comparable groups due to study design. Included cohort studies evaluated by JBI appraisal tool generally reported clear inclusion criteria, participant demographics, and outcomes. Nonetheless, consecutive, and complete patient inclusion was often uncertain.

Baseline Characteristics

Study characteristics are listed in Table 1. The included studies originated from 13 countries on 4 continents, with 19 of these originating from the same region. The study populations were heterogeneous regarding BMI. The median follow-up was 12 months (12–60 months). Across studies, the definitions of remission of T2DM, and choice of weight loss outcome varied substantially, Table S1. Further, differences existed in details of the surgical technique, such as the size and position of the anastomosis and the length of the common channel.

Outcome Measures

Results for the evidence certainty of the outcome measures of the comparative studies, including GRADE evaluation are graphically presented in Appendix C.

SASI vs. SG

Weight Loss

One RCT [22] reported a MD in %EWL of 17% (95% confidence interval [CI] −2.5 to 36.0), Fig. 2a, the certainty of evidence is very low by GRADE evaluation. Three NRCTs [25–27] provided %TWL, identifying a MD of 2.2% (CI −0.27 to 4.6), Fig. 2b, the certainty of evidence is very low.

Fig. 2.

Forest plots of weight loss measures in the comparative studies of SASI vs. other common bariatric procedures at 1-year follow-up. Note. SASI single-anastomosis sleeve ileal bypass, %EWL percentage excessive weight loss, SG sleeve gastrectomy, RCT randomized controlled trial, NRCT non-randomized comparative studies, %TWL percentage total weight loss, OAGB one anastomosis gastric bypass, RYGB Roux-en-Y gastric bypass

T2DM

All 5 studies comparing SASI with SG reported remission of T2DM. One RCT [22] found a risk ratio (RR) of 1.92 (CI 1.26–2.94), Fig. 3a, the certainty of evidence is low. Meta-analysis of the NRCTs [25–28] showed a RR for remission of T2DM of 1.20 (CI 0.95–1.50), Fig. 3b, the certainty of evidence is very low.

Fig. 3.

Forest plots of remission of type 2 diabetes mellitus after SASI vs. other common bariatric procedures at 1-year follow-up. Note. T2DM type 2 diabetes mellitus, RCT randomized controlled trial, NRCT non-randomized comparative trials, SASI single-anastomosis sleeve ileal bypass, SG sleeve gastrectomy, OAGB one anastomosis gastric bypass, RYGB Roux-en-Y gastric

Dyslipidemia

Three NRCTs [25, 27, 28] reported remission of dyslipidemia with a RR of 1.29 (CI 1.01 to 1.65), Figure S1a, the certainty of evidence is very low.

Nutritional Parameters

Levels of albumin and vitamin B12 at 1-year was reported by two NRCTs [25, 27] with no difference detected, Table S2. One NRCT [27] found lower levels of vitamin D after SASI than SG, MD −6.7 (units not reported) (CI −8.9 to −4.6), Figure S2a, the certainty of evidence is very low.

Complications

One NRCT [25] reported a difference in early complication rate of 4% for SASI vs. 0% for SG (p = 0.07), and 12-month complication rate of 14.9% for SASI, and 2% for SG (p = 0.005). Clavien-Dindo class II for 13 patients, and class III for 1 patient in the SASI group, and class II for 2 patients in the SG group. Another NRCT [28] reported a complication rate of 26.3% for SASI and 0.95% for SG after 12 months (p not stated).

SASI vs. OAGB

Weight Loss

%TWL was reported by two NRCTs [25, 27] which were included in the meta-analysis, finding a MD of 4.5% (CI −0.53 to 9.4), Fig. 2c, the certainty of evidence is very low.

Two RCTs [23, 24] comparing SASI to OAGB did not include uncertainty measures for weight loss and could not be included in meta-analysis. One of these [23] reported a difference in mean %EWL at one year of 76.5% for SASI and 86.5% for OAGB, p = 0.045. In contrast, the other RCT [24] reported a difference in mean %EWL of 67.2% for SASI vs. 61.8% for OAGB, p = 0.054. One NRCT [29] reported a mean % excessive BMI loss (range) at one year of 79.3% (40–178.7%) for SASI vs. 75.6% (33.4–188%) for OAGB; p = 0.015.

T2DM

Three NRCTs [25, 27, 28] reported T2DM remission for SASI vs. OAGB with a RR of 1.01 (CI 0.84 to 1.21), Fig. 3c, the certainty of evidence is very low.

Dyslipidemia

Three NRCTs [25, 27, 28] observed remission of dyslipidemia, and meta-analysis gave a RR of 1.01 (CI 0.80 to 1.27), Figure S1b, the certainty of evidence is very low.

Nutritional Parameters

Albumin at 1-year was reported by 1 RCT and 3 NRCTs [24, 25, 27, 29], Hb by 2 RCTs and 1 NRCT [23, 24, 29], and ferritin by one NRCT [23] with no differences detected, Table S2. One NRCTs [27] found lower levels of vitamin D after SASI than OAGB, MD −12 (units not reported) (CI −18 to −6.8), Figure S3b. One RCT [23] and two NRCTs [25, 27] identified higher levels of vitamin B12 for SASI than OAGB with std.MD 0.92 (CI 0.39 to 1.44) and 0.53 (CI 0.25 to 0.78) respectively, Figure S3c and d. All findings were graded as very low evidence except for higher levels of vitamin B12 in patients after SASI in the RCT [23] (low evidence).

Complications

One NRCT [25] reported early complication rates of 4% for SASI vs. 1% for OAGB (p = 0.07), and 12-month complication rates of 14.9% for SASI and 9.8% for OAGB (p = 0.005). Complications were Clavien-Dindo class II for 13 patients, and class III for 1 patient in the SASI group, and class II for 9 patients and class III for 1 patient in the OAGB group. Another NRCT [28] reported a complication rate of 26.3% for SASI and 5.1% for OAGB (p not stated).

SASI vs. RYGB

Weight Loss

Two NRCTs [30, 31] compared SASI to RYGB. %EWL was reported by both studies with the finding of a MD of 4.2% (CI −4.1 to 13), Fig. 2d, the certainty of evidence is very low.

T2DM

T2DM remission for SASI vs. RYGB was reported by the same NRCTs [30, 31] giving a RR of 1.01 (CI 0.97 to 1.06), Fig. 3d, the certainty of evidence is very low.

Dyslipidemia

Reported remission of dyslipidemia by the two NRCTs [30, 31] gave a RR of 0.94 (CI 0.74 to 1.2), Figure S1c, the certainty of evidence is very low.

Nutritional Parameters

Albumin at 1 -year was reported by 1 NRCT [31] and vitamin B12 by another NRCT [30] with no detected difference between SASI and RYGB, Table S2. Hb was reported by both studies and were higher after SASI than RYGB, MD 1.1 g/dL (CI 0.56 to 1.5). Ferritin was reported by one NRCT [30] with higher levels for SASI than RYGB, 25 µg/L (CI 12 to 38), Table S2 and Figure S3e. Vitamin D was not reported, the certainty of evidence is very low.

Complications

One NRCT [31] presented a complication rate of 13% up to 12 months for SASI and 4.3% for RYGB (p = 0.27).

Clinical Outcomes After SASI Across Comparative and Non-comparative Studies

Weight loss

Twenty-three studies reported mean BMI results after SASI, with a preoperative range of 38 to 58 kg/m² and a BMI range at 1-year follow-up of 22.6 to 33.8 kg/m². At 1-year follow-up, 11 studies presented mean %TWL ranging 28–44%, and a pooled cross-study mean %TWL of 35.9% (CI 32 to 40%) was calculated as descriptive summary without adjustment for study design or case-mix, Figure S3. Six studies presented results beyond 1 year (24 to 60 months) with sustained weight loss effects, but with a decreasing number of patients, Table S3.

T2DM

Twenty-two studies examined the effects of SASI on T2DM with a remission rate ranging from 32% to 100%. An analysis of the 21 studies reporting ratios showed a pooled mean probability of T2DM remission of 0.91 (CI 0.85 to 0.96), Table S4.

Dyslipidemia

Sixteen studies reported the effect on the presence of dyslipidemia with remission rates in the range of 70–100%. Single-arm analysis of 14 studies reporting ratios showed a pooled mean probability of remission of 0.91 (CI 0.84 to 0.96), Table S5.

Nutritional Parameters

Changes in nutritional parameters are listed in Table S6. Substantial heterogeneity existed across studies with some indicating decreases in markers such as albumin, hemoglobin, and ferritin, while vitamin D and vitamin B12 showed larger variability. A formal meta-analysis was not performed for these parameters because the level of detail required would exceed the scope and aims of this systematic review.

Complications

Across all SASI cohorts, 5 studiespresented structured reporting of complications after surgery according to the Clavien-Dindo (CD) classification [25, 36, 39, 45, 46]. These studies included 638 patients and reported 8 grade I complications (1.2%), 28 (4.4%) grade II complications, 34 (5.3%) grade III complications, and 1 (0.15%) grade IV complication.

Across studies there were no reported deaths during follow-up. The rate of early (< 30 days) complications ranged from 0 to 30.8%. Twenty-one studies reported on rate of reoperations during the follow-up. These studies included 1 698 patients and 99 reoperations (5.8%) for a follow-up of median 12 months (range 12–60 months). Indications and procedures are summarized in Table 2.

Table 2.

Reoperations after SASI across studies in 1698 patients with a median follow-up of 12 months

Indication	No (%)	Procedure
Diarrhea, hypoalbuminemia, excessive weight loss, and one case of twisting of the biliopancreatic limb	41 (2.4)	Conversion to SG
Gastroesophageal reflux	5 (0.3)	Conversion to RYGB
Internal herniation	3 (0.2)	Closure of mesenteric defects
Anastomotic leak (6) or stenosis/ulcer (8)	14 (0.8)	Revision of anastomosis
Intraabdominal bleeding	14 (0.8)	Hemostatic surgery
Port site hernia	4 (0.2)	Hernia operation
Small bowel obstruction	2 (0.1)	Adhesiolysis
Cholecystolithiasis	16 (0.9)	Cholecystectomy
Total number of reoperations	99 (5.8)

SG sleeve gastrectomy, RYGB Roux-en-Y gastric bypass

Discussion

This systematic review aimed to evaluate the effectiveness of SASI compared to other surgical- or non-surgical treatments. We identified 1 RCT and 4 NRCTs comparing SASI to SG, 2 RCTs and 4 NRCTs comparing SASI to OAGB, and 2 NRCTs comparing SASI to RYGB. Most studies reported outcomes at 12 months. Using the GRADE approach, we are very uncertain whether there is any difference in weight loss between SASI and SG, OAGB and RYGB. For remission of T2DM, SASI may result in better outcomes compared to SG (RR 1.92, 95% CI 1.26 to 2.94; 1 RCT, 51 patients; low-certainty evidence). Remission of dyslipidemia was higher for SASI than SG (RR 1.29, 95% CI 1.01 to 1.65, 3 NRCTs, 138 patients) but we are uncertain of the results due to very low certainty of evidence. We are very uncertain whether there is any difference in diabetes remission between SASI and OAGB or between SASI and RYGB (very low-certainty evidence). For nutritional outcomes we are very uncertain whether there is any difference in outcomes. We did not perform GRADE evaluation for complication rates. Higher complications rates (> 30days) were reported after SASI than after SG and OAGB, mostly Clavien-Dindo class II complications. No difference was reported for short-term complications in SASI vs. RYGB. Overall, our confidence in the findings was substantially limited by imprecision due to small studies with few participants, risk of bias, and considerable heterogeneity, precluding definitive conclusions about the comparative effectiveness of these surgical procedures.

Effectiveness of the SASI procedure was evaluated in two recent systematic reviews by Ataya et al. and Oliveiro et al. [9, 10]. Ataya et al. reported a mean weight loss of 35.2% (CI 32.3 to 38.0) and a T2DM remission rate of 88.3 (CI 79.7 to 95.0) following SASI, which is nearly identical to the %TWL of 35.9%, and the T2DM remission rate of 91% demonstrated in our single-arm meta-analyses. Oliveira reported a greater weight loss with SASI than SG, a finding that was not replicated in our study. While the effect estimates in our analyses suggested a possible weight loss benefit of SASI compared to SG, the confidence interval crossed the line of no effect, indicating statistical uncertainty. Five studies included by Oliveira were excluded in our review due to more restrictive inclusion criteria of ≥ 20 patients, SASI only as primary surgery, and no overlapping populations.

Oliveira reported a higher remission rate of T2DM after SASI than SG similar to one RCT [22] comparing SASI to SG. The remission rates of T2DM were not significantly different in the NRCTs, studies, possibly due to different patient characteristics in the non-randomized trials. Like Oliveira, we found that remission rates of dyslipidemia were higher for SASI than SG but not significantly different for OAGB or RYGB. The certainty of the evidence was rated as low to very low according to the GRADE approach, underscoring substantial limitations in the underlying data.

Malnutrition and hypoalbuminemia remain a concern with some studies presenting alarming results after SASI with revision rates of 20–50% [32, 33]. Previous systematic reviews reported hypoalbuminemia in the range of 1.5–5% [9, 10]. We found no difference in albumin levels between SASI and SG, OAGB or RYGB at 1 year follow-up with very low certainty of evidence. Nutritional concerns often manifest later than 1-year post-surgery, which limits the long-term significance of these early findings and warrants long-term monitoring of patients after SASI. Surgical takedown of the ileal loop due to malnutrition was performed in a relatively small proportion (2.4%) of patients in this review.

Reporting of complications following SASI varied substantially. Reported Clavien-Dindo III - IV complication rates (5.8% and 0.18%) across studies, were in line with those after other bariatric procedures. However, such data were reported in only 4 of 26 studies, after median 12-month follow-up, and they should be interpreted with considerable caution.

Considerable heterogeneity existed in the surgical techniques, including size of the anastomosis, position on the sleeve, and the length of the common channel, Table S1. These technical factors could potentially influence both weight loss outcome and complication rates. A recent publication identified shorter common channel of 250 cm and size of anastomosis >3 cm to be risk factors of malnutrition [34]. Patients who had a common channel of 350 cm had a 10-year %EWL of 63%, in line with the sustained long-term weight loss in the present paper, Table S3.

This review adhered to PRISMA guidelines, was prospectively registered in PROSPERO, and included seven studies published after 2023, ensuring that the most recent evidence on the SASI procedure was captured. The inclusion of both RCTs and cohort studies allowed for a broader understanding of the procedure’s early implementation and real-world outcomes. The use of the GRADE approach provided a transparent assessment of the certainty of evidence. We performed both comparative and single-arm analyses. While the comparative analyses provide the most reliable evidence for clinical decision-making, the addition of single-arm analyses offer supplementary information about the absolute effectiveness of SASI, which may be useful given the limited evidence base for this novel procedure.

This review, however, has review important limitations. The evidence base consisted of few, small studies with substantial methodological limitations, resulting in small patient samples for each comparison. Considerable heterogeneity was evident across studies regarding patient characteristics, baseline T2DM prevalence, and surgical technique (particularly limb lengths). Although sensitivity analyses based on study quality and subgroup analyses exploring these sources of heterogeneity would have strengthened our findings, the limited number of studies per comparison precluded such analyses. Risk of bias was assessed at the study level rather than for individual outcomes, which may have resulted in underestimation of bias for some outcomes. Few studies reported outcomes longer than 12 months, which limited our ability to assess medium-term effectiveness.

Although the review included a relatively broad range of outcomes, not all relevant outcomes were assessed. For example, patient-reported measures such as quality of life were not included in the review, which may limit the comprehensiveness of the findings.

In conclusion, we believe that SASI might represents a novel MBS procedure of interest, as earlier studies have indicated favorable effects on weight loss and improvement of metabolic diseases, and it offers the anatomical advantage of preserving endoscopic access to the stomach and biliary system. Nevertheless, this systematic review highlights that the current evidence remains insufficient to establish the comparative effectiveness of SASI against other bariatric procedures, as the available studies are few, small, and have substantial methodological limitations. In line with the IFSO statement the procedure should still be regarded as investigational; ideally conducted as part of a clinical trial or dedicated registry, with unbiased information to the patients about the innovative nature, potential risks, benefits, and existing alternatives [8].

To strengthen the evidence base, future research should prioritize high-quality, adequately powered RCTs with standardized surgical techniques and structured nutritional follow-up. Consistent reporting of standardized outcome measures—such as those recommended by the American Society for Metabolic and Bariatric Surgery [35]—is essential for improving comparability across studies and guiding clinical decision-making in bariatric surgery.

Supplementary Information

Below is the link to the electronic supplementary material.

Authors’ Contributions

H.M.H contributed to the conceptualization and development of the study design, performed the primary and full-text screening of articles, bias assessment, data curation, and formal analysis, and drafted the original version of the manuscript. T.T.S contributed to the conceptualization of the study, participated in the full-text screening of articles and bias assessment, and was involved in reviewing and editing the manuscript. H.R contributed to the study structure, methodology, data analysis, and software development, and provided extensive critical review of the manuscript. R.E.H assisted with data presentation and preparation of tables and contributed to the critical review of the manuscript. T.M and J.A.K contributed to the conceptualization of the study and provided critical review and supervision throughout manuscript development. All authors read and approved the final version of the manuscript.

Funding

Open access funding provided by University of Oslo (incl Oslo University Hospital)

Data Availability

All original data used in this systematic review were extracted from previously published studies and are available directly in those source articles. The data collection forms, extracted datasets, and complete analysis code are not publicly deposited but are available from the corresponding author upon reasonable request. No new data were generated or analyzed beyond what is reported from the original publications.

Declarations

Competing interests

The authors declare no competing interests.