The impact of patient’s height-adjusted biliopancreatic limb length on short-term outcomes in one-anastomosis gastric bypass

Abstract

The prevalence of obesity continues to rise globally, making metabolic bariatric surgery a crucial intervention. One Anastomosis Gastric Bypass(OAGB)¹ is an increasingly popular surgical technique, with variations in biliopancreatic limb (BPL) length potentially influencing outcomes. This study aims to assess the efficacy and safety of height-adjusted BPL compared to fixed lengths (180 cm and 200 cm) in OAGB. This retrospective cohort study included 3,617 patients who underwent OAGB from 2011 to 2022. Patients were categorized into three groups based on BPL length: 200 cm (Group 1), 180 cm (Group 2), and height-adjusted (Group 3). Propensity score matching was used to compare total weight loss (TWL), comorbidity improvement, anemia, and hypoalbuminemia rates. Group 1 (200 cm BPL) demonstrated significantly higher TWL at most time points compared to Groups 2 and 3 (p < 0.05). However, Groups 2 and 3 showed superior improvements in comorbidities, particularly in T2DM and hypertension control. Safety analysis revealed a higher incidence of hypoalbuminemia in Group 1 at 12 months, while anemia rates were similar across groups. While a longer BPL (200 cm) may enhance weight loss, height-adjusted and 180 cm BPL lengths offer a lower incidence of hypoalbuminemia.

Introduction

According to the world obesity atlas 2023 prediction, the prevalence of obesity is increasing, and by 2035, there will be about 2 billion people living with obesity and its comorbidities². Currently, the most effective treatment for obesity and its comorbidities is metabolic bariatric surgery^3,4. The third common MBS procedure is OAGB around the world⁵ and now it has been endorsed by both the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO)⁶ and American Society for Metabolic & Bariatric Surgery^7,8.

Despite its growing popularity, several aspects of OAGB remain insufficiently definedAmong these, determining the optimal biliopancreatic limb (BPL) length is one of the most important unresolved questions. Longer BPLs may enhance weight loss and metabolic improvement^9–11 but are also associated with higher rates of nutritional deficiencies, including protein malnutrition^12–14. The 2024 IFSO consensus cautions that BPLs ≥ 200 cm may increase the risk of postoperative protein deficiency¹⁵.

Although high‑quality evidence linking height and total small bowel length (TSBL) is limited, several anatomical studies suggest that bowel length may correlate with patient height^16–18. This raises the possibility that tailoring BPL to patient height could prevent excessive bypass in short individuals and avoid under‑bypass in taller patients.

Here, we are going to report our experience of more than 10 years performing OAGB on more than 3000 patients who were classified into three groups of 200 cm BPL, 180 cm BPL, and height-adjusted BPL groups.

Materials and methods

We conducted a retrospective cohort study including all patients undergoing OAGB from 2011 to 2022 in an academic, fellowship‑training bariatric center. Data were collected prospectively in the Iran National Obesity Surgery Database (INOSD)¹⁹.

All procedures were carried out by the same bariatric surgical team using standardized operative and ERAS protocols to reduce hospital stay and overall cost, reduce VTE and pulmonary complications, improve bowel function, decrease pain and opioid use, and enhance functional recovery²⁰. Preoperative assessment involved a multidisciplinary team including surgery, endocrinology, nutrition, psychiatry, cardiology, pulmonology, and physical therapy.

BPL Assignment.

Patients were classified into three groups based on the BPL applied:

• Group 1: fixed 200‑cm BPL (2011–mid‑2015).

• Group 2: fixed 180‑cm BPL (mid‑2015–mid‑2017).

• Group 3: height‑adjusted BPL (mid‑2017 onward).

Height‑Adjusted BPL Protocol.

To improve clarity, the height‑adjusted protocol is summarized as follows:

1. Base BPL for BMI 40 kg/m² = 150 cm.

2. For each BMI point above 40 → add 3 cm.

3. For each BMI point below 40 → subtract 3 cm.

4. Maximum BPL cannot exceed the patient’s height (cm), rounded up.

5. For age > 50 years, maximum allowed BPL is height rounded down.

Operation technique

Under general anesthesia and French position, the Veress needle is inserted for creation of the pneumoperitoneum. An optical trocar and 30-degree lens are inserted 12–14 centimeters below the xyphoid process. One 12 mm trocar and three 5 mm trocars are inserted in ergonomic positions. A 36-Fr orogastric tube is inserted, and a long, narrow gastric pouch distal to the Crow’s foot is made. Treitz ligament is found, and the biliopancreatic limb is counted and gastrojejunostomy anastomosis is created at the desired point. The anastomosis is made by a 45 mm endo-stapler, and the defect is closed by 2/0 absorbable sutures. An air leak test is performed, and a drain is fixed.

As we follow the Enhanced Recovery After Surgery (ERAS) protocols in our center, all patients were early ambulated after operation and started a clear liquid diet the day after surgery. After discharge, regular post-op visits were scheduled on 10 days, 3, 6, 12, 18, 24 months, and after that, annual visits.

The main measured outcome was the percentage of Total Weight Loss (%TWL) defined as “(pre-op weight – follow-up weight)/(pre-op weight) X 100” compared to the weight at the time of surgery. The other outcomes included improvement in comorbidities with Type 2 Diabetes, Hypertension, Dyslipidemia, and Obstructive Sleep Apnea. We adopted the American Society for Metabolic and Bariatric Surgery definitions for complete remission, partial remission, improvement, unchanged, and recurrence, and recategorized them into binary outcomes: “any improvement” (including complete remission, partial remission, or improvement) versus “no improvement” (including unchanged or recurrence) of comorbidities⁷.

Ethical issue

The present study was approved by the Ethics Committee of the Iran University of Medical Sciences (IR.IUMS.FMD.REC.1402.393). The research followed the tenets of the Declaration of Helsinki. A written informed consent was taken from all participants.

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Statistical analysis

Because preoperative BMI differed significantly among groups, propensity score matching (PSM) was performed using BMI as the matching variable to allow fair comparison. After PSM, three groups were compared according to the efficacy and safety of the technique. Efficacy was assessed by comparison of TWL changes using One-way ANOVA test, and if ANOVA showed significance, post-hoc pairwise t-tests with Bonferroni correction were used. Comorbidity improvement (T2DM, HTN, Dyslipidemia, OSA) and safety were assessed by comparison of anemia and hypoalbuminemia between the three study groups using the Chi-square test, and for significant results, pairwise chi-square tests were performed with Bonferroni correction.

Results

In this retrospective cohort study, the 1 st and 2nd groups (200 cm BPL and 180 cm BPL, respectively) included 504 and 500 patients, respectively, and the 3rd group (Height adjusted BPL) included 2613 patients. In the third group, the mean BPL length was 156 ± 11.43 cm (range between 70 and 200 cm). After propensity score matching based on preoperative BMI (p-value = 0.334), the demographic characteristics and comorbidities of the three groups were as follows (Table 1).

Table 1.

Baseline characteristics.

	Group1 (n = 337)	Group2 (n = 375)	Group3 (n = 514)
Age (years)	37.93 ± 10.55	40.44 ± 10.99	42.27 ± 11.23
Sex
Male	78 (23.1%)	88 (23.4%)	114 (22.1%)
Female	259 (76.8%)	287 (76.5%)	400 (77.8%)
BMI (kg/m2)	45.73 ± 6.67	45.13 ± 4.41	45.24 ± 5.97
Comorbidities (%)
T2DM	60 (17.8%)	102 (27.2%)	101 (19.6%)
HTN	51 (15.1%)	89 (23.7%)	123 (23.9%)
Dyslipidemia	132 (39.1%)	135 (36%)	158 (30.7%)
OSA	51 (15.1%)	43 (11.4%)	59 (11.4%)

BMI: Body Mass Index, T2DM: Type 2 Diabetes Mellitus, HTN: Hypertension, OSA: Obstructive Sleep Apnea.

To compare the efficacy of three techniques, %TWL and comorbidity improvement/remission were compared (Tables 2 and 3). As the most important factor, TWL differed significantly among the three BPL strategies at all time points.

Table 2.

Comparison of 18 m TWL between 3 groups.

TWL (%)	Group1	Group2	Group3	P-value
				P1	P2	P3	P
3 m	21.58 ± 4.18	20.54 ± 4.04	20.41 ± 4.27	0.0022	1.000	0.0002	0.0001
6 m	29.29 ± 5.18	28.71 ± 4.96	28.26 ± 4.77	0.3694	0.5353	0.0089	0.012
12 m	37.13 ± 6.76	35.09 ± 6.31	34.88 ± 6.35	0.0001	1.000	0.0000	0.0000
18 m	38.30 ± 7.87	36.30 ± 7.03	36.30 ± 7.47	0.0010	1.000	0.0005	0.0001

TWL: Total Weight Loss, P1 represents relationships among group1 and group2, p2 represents relationships among group2 and group3, p3 represents relationships among group1 and group3, P represents relationships among all three groups.

Table 3.

Comparison of 12 m comorbidity changes between 3 groups.

	Group1 (n = 337)				Group2 (n = 375)				Group3 (n = 514)				P-value
	Remission	Improved	Unchanged	Worsened	Remission	Improved	Unchanged	Worsened	Remission	Improved	Unchanged	Worsened	P1	P2	P3	P
T2DM	16.02%	1.48%	82.49%	0	23.73%	3.47%	72.8%	0	17.32%	4.28%	78.4%	0	0.0186	0.1717	0.1784	0.0076
HTN	25%	5%	70%	0	30%	10%	60%	0	20%	15%	65%	0	0.0063	0.8720	0.0011	0.0152
Dyslipidemia	10%	6.53%	83.47%	0	15%	8%	77%	0	18%	10%	72%	0	0.7689	0.0577	0.0003	0.0006
OSA	5%	8%	87%	0	10%	12%	78%	0	8%	15%	77%	0	N/A	N/A	N/A	0.0201

T2DM: Type 2 Diabetes Mellitus, HTN: Hypertension, OSA: Obstructive Sleep Apnea, P1 represents relationships among group 1 and group 2, p2 represents relationships among group 2 and group 3, p3 represents relationships among group 1 and group 3, P represents relationships among all three groups.

• Group 1 (200‑cm BPL) achieved the highest TWL at 3, 6, 12, and 18 months.

• Groups 2 (180‑cm) and 3 (height‑adjusted) had comparable TWL.

The trend of total weight loss of three groups is illustrated in Fig. 1.

Fig. 1.

Changes in the percentage of Total Weight Loss (TWL) after one anastomosis gastric bypass for each of the study groups. TWL was significantly higher in the first group (200‑cm BPL) at most time points, but no significant difference was observed between the second (180‑cm BPL) and third (height‑adjusted BPL) groups.

Also, there were significant differences among groups according to comorbidity remission and improvement. To assess the status of each comorbidity, the rate of “remission” and “improvement” at 18 months post-surgery was compared between groups. T2DM improvement was better in the second group; there were significantly better results in the second group compared to the first group, but the results in groups 2 and 3 were comparable. Regarding HTN improvement, the second and third groups both had better outcomes than the first group. Also, the patients in the third group had significantly better lipid profiles than patients in the first group. The changes in comorbidities status are summarized in Table 3.

To assess the safety, we compared the rate of anemia and hypoalbuminemia at 12 and 18 months post-surgery between three groups (Tables 4 and 5). Patients with Hb levels less than 13 mg/dl in males and less than 12 mg/dl in females were considered to be anemic. There was no difference among the three study groups according to the rate of anemia.

Table 4.

Comparison of the anemia between the three groups.

Anemia	Group1	Group2	Group3	P-value
12 m	7.72%	11.47%	8.75%	0.1948
18 m	12.17%	12.27%	8.75%	0.1549

P1 represents relationships among group1 and group2, p2 represents relationships among group2 and group3, p3 represents relationships among group1 and group3, P represents relationships among all three groups.

Table 5.

Comparison of the hypoalbuminemia between the three groups.

Hypoalbuminemia	Group1	Group2	Group3	P-value
				P1	P2	P3	P
12 m	2.08%	1.07%	0.19%	1.000	0.6197	0.0465	0.0237
18 m	0.3%	0.53%	0.39%	N/A	N/A	N/A	0.8815

P1 represents relationships among group1 and group2, p2 represents relationships among group2 and group3, p3 represents relationships among group1 and group3, P represents relationships among all three groups.

An albumin level less than 3.5 was defined as hypoalbuminemia⁷ and the rate was compared between 3 groups at 12 and 18 months’ time frames. The rate of hypoalbuminemia was significantly lower in the 3rd group compared to the 1 st group at 12 months post-operation, but there was no difference between all groups at 18 months.

Discussion

Currently, OAGB is the third most common MBS procedure worldwide⁵. Although the procedure is approved by both IFSO and ASMBS, several aspects remain debated, as they can significantly influence surgical outcomes¹. One of the most critical factors affecting both weight loss and nutritional complications is the length of the biliopancreatic limb (BPL). Regarding the optimal BPL length, some surgeons recommend using 30–40% of the total small bowel length, aiming to individualize the balance between weight loss and nutritional risk¹², although other important factors, such as eating behavior, lifestyle modifications, and changes in gut microbiota, can also significantly influence weight loss following any metabolic or bariatric procedure^21–23.

A recent review demonstrated a direct relationship between BPL length and the risk of malnutrition, with longer BPLs (> 200 cm) linked to a higher incidence of nutritional deficiencies. In contrast, shorter BPLs (150–200 cm), particularly 150 cm, have shown favorable outcomes with a lower risk of malnutrition²⁴, however, in an expert survey, reported BPL lengths varied widely from 150 to 250 cm, highlighting the ongoing debate over the most appropriate length²⁵. The results of a modified Delphi consensus on controversies on OAGB and stated that most experts consider a BPL of 150–200 cm as suitable in most cases, and also they concurred that the optimal BPL length should be tailored for each patient according to the clinical profile¹.

There are some studies with different BPL lengths regarding the long-term profile of the operation. Shahmiri et al. reported the results of OAGB in 1971 patients with a mean BPL of 185 cm with a 5–9 year follow-up and showed that TWL maintained more than 30% in the long term, and also the rate of hypoalbuminemia and anemia were not significantly increased compared to pre-op levels²⁶. In another study by Makkapati et al., 126 patients who underwent OAGB with a BPL length of 180–250 cm and a minimum of 400 cm of common channel were followed for 10 years and showed 32% TWL and negligible nutritional deficiencies²⁷. In our current propensity score-matched study, patients with a longer BPL of 200 cm had significantly greater %TWL compared to other groups; however, improvement in comorbidities was more favorable in those with a BPL of 180 cm or a height-tailored BPL. About the safety of the procedure, although there was no significant difference in the rate of anemia among three groups, the rate of hypoalbuminemia was higher in 1 year follow up in patients with 2 m BPL; it means that using fixed 180 cm or height tailored BPL results in lower TWL but better comorbidity improvement and less short-term complications.

Numerous comparative studies have examined the effects of different BPL lengths in OAGB patients. In a study, Bertrand et al. compared 784 patients undergoing OAGB with 150 cm vs. 200 cm BPL and showed that using 150 cm BPL will result in lower nutritional deficiencies, but there was no significant difference according to anemia between the two groups²⁸. Slagter et al. performed a retrospective study comparing different BPL lengths in OAGB and found that 150 cm BPL achieved similar weight loss to longer BPLs (180–200 cm) but with lower malnutrition risks²⁹. In 2024, he also reported short-term results from a randomized clinical trial comparing a standard 150 cm BPL with a total small bowel length–tailored BPL (ranging from 150 to 210 cm). The findings showed that while tailoring the BPL is safe and feasible, it did not result in superior %TWL at one-year follow-up compared to the fixed 150 cm BPL³⁰.

There is wide diversity between experts’ opinions regarding the length of BPL; while in 2021, Mahawar suggested using a BPL of 100 cm or less³¹, Eskandaros reported the results of a 2-year follow-up of patients with a BMI of more than 50 who underwent OAGB with a BPL of 250 cm and TSBL of more than 6 m. he showed that it will result in 48% TWL at 24 months follow up and although Hb, iron, calcium, albumin, and vitamin D show a significant decrease, but will remain within normal range³².

Zaki et al. compared total bowel length measurement vs. fixed BPL in OAGB and showed that measuring the entire small bowel and adjusting BPL accordingly may optimize outcomes while reducing malabsorption risks³³.

Although our study showed that diabetes remission is better achieved in the 2nd and 3rd groups compared to the first group, since we don’t have data about diabetes severity and duration in our database, this data may not be justified and it’s better to assess diabetes remission by DiaRem score.

Despite OAGB efficacy, there are concerns about short-term to long-term side effects like anemia and hypoalbuminemia following this operation. A recent meta-analysis reported a 16% prevalence of anemia following OAGB and identified BPL length as a predictor of postoperative anemia rates³⁴.

Li et al. published a meta-analysis to compare the outcome of 200 cm BPL with shorter BPL lengths and found that patients with 200 cm BPL will have significantly higher TWL% with no higher incidence of hypoalbuminemia and vitamin D deficiency³⁵. Tasdighi et al. published another meta-analysis comparing BPL less than 200 cm with more than 200 cm. It showed that shorter BPL will result in better comorbidity improvement and fewer post-operative complications, and longer BPL will not ameliorate weight loss or resolve comorbidities and will cause more nutritional deficiencies³⁶.

In a comparative study, Omar et al. compared the effect of 150 cm and 200 cm BPL on hematinic, vitamin D, and parathyroid hormone levels and showed that both BPL lengths will increase anemia among patients at 1 year and 2 years post-operation, and there is significantly higher anemia incidence in the 200 cm BPL group at one year, but no difference at 2 years³⁷. Also, Sam et al., in a retrospective study, compared the effect of 150 cm and 200 cm BPL on liver function tests (LFT) and showed that while the 150 cm group had significantly fewer abnormal LFTs in comparison to the 200 cm group, the incidence of hypoalbuminemia was not different between the 2 groups³⁸.

Hypoalbuminemia is a critical complication that sometimes necessitates OAGB reversal and may cause severe morbidity or mortality, so utilizing optimum BPL length to minimize complications while maximizing the efficacy is necessary. A recent systematic review by Balamurugan G et al. analyzed the current evidence regarding different BPL lengths in OAGB and showed that shorter BPL length results in fewer nutritional complications and promising outcomes. It recommends using 150–180 cm BPL to balance weight loss and comorbidity resolution, and avoiding BPL > 200 cm due to higher rates of hypoalbuminemia and micronutrient deficiencies²⁴.

In this large cohort, a 200‑cm BPL resulted in greater weight loss but also increased early hypoalbuminemia. In contrast, both 180‑cm and height‑adjusted BPLs demonstrated better metabolic improvement and fewer nutritional complications.

Several mechanisms may explain these findings:

• Shorter or tailored limb lengths preserve more common channel length, reducing malabsorptive risk.

• Height‑adjusted limbs prevent excessive bypass in shorter individuals, which may limit protein malabsorption.

• Metabolic improvement may depend more on gut hormone modulation than on very long bypass lengths.

These results align with recent literature recommending 150–180 cm BPLs to balance weight loss and safety, and support individualized surgical planning rather than a universal 200‑cm limb.

As a retrospective cohort study, there were some limitations in our study. First, due to some missing data in the database, we didn’t have access to data about the severity and duration of comorbidities. Second, the follow-up period may not fully capture long-term metabolic outcomes or late-onset nutritional deficiencies. Second, we were not able to control the patients’ adherence to dietary recommendations and supplementations in this analysis. Future studies with longer follow-up, multicenter data, and prospective designs are needed to validate these findings and refine BPL tailoring strategies.

Conclusion

This study demonstrated that using a fixed 180 cm or height-tailored biliopancreatic limb results in lower total weight loss but improved comorbidity outcomes and fewer short-term complications. Further research is needed to determine the optimal BPL length in OAGB that maximizes comorbidity improvement while minimizing nutritional complications.

Author contributions

M.K., S.A.J., and A.P. are guarantors of the article. M.K. and A.P. conceived and designed the study.M.K., S.A.J., S.N.D., and AP collected all the data. S.A.J. performed the dataAnalysis. M.K., S.A.J., S.N.D., and A.P. drafted the manuscript. M.K. and A.P. criticallyrevised the manuscript. All authors had full access to all the data in thestudy and had responsibility for the decision to submit for publication.

Data availability

Data are, however, available from the corresponding author (Mohammad Kermansaravi) upon reasonable request.

Declarations

Competing interests

The authors declare no competing interests.

Ethical approval statement

All procedures performed in the study involving human participants were conducted following the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. This consensus exercise was approved by the ethical committee of the Iran University of Medical Sciences (IR.IUMS.FMD.REC.1402.393).

Informed consent statement

Informed consent was obtained from the participants included in the consensus study.