The Future of Bariatric Surgery Research: A Worldwide Map of Upcoming Clinical Trials

Table of Contents

• Key Points
• Background: Why This Research Matters
• Study Methods: How the Research Was Conducted
• Key Findings: What the Research Revealed
• Clinical Implications: What This Means for Patients
• Limitations: What This Study Couldn't Tell Us
• Recommendations: A Roadmap for Future Research
• Frequently Asked Questions
• Source Information

Key Points

• A 2021 registry review found 62 upcoming randomized bariatric surgery trials planning about 10,800 participants.
• Sleeve gastrectomy and Roux-en-Y gastric bypass were each studied in 39 trials, the most of any procedure.
• Obesity-related diseases, especially type 2 diabetes, are now the most frequent focus, appearing in over 80% of trials.
• More than half of the upcoming trials follow patients for one year or less; only 23% exceed four years.
• Researchers recommend longer follow-up and more research on nutritional deficiencies, muscle loss, and mental health after surgery.

Background: Why This Research Matters

Obesity has grown to pandemic proportions worldwide since the early 1980s, with more than 2 billion people now affected. Among the available treatment options, bariatric surgery (weight-loss surgery) remains one of the most effective treatments for patients with severe obesity who are committed to lifelong nutritional follow-up. Studies have shown that bariatric surgery leads to an increase in life expectancy, making it a cornerstone of care for carefully selected patients.

The history of bariatric surgery dates back to 1950, and since then, hundreds of papers have been published on the topic. Some surgical techniques have stood the test of time, while others have been abandoned. At the same time, innovative procedures are continually being developed, such as sleeve gastrectomy with transit bipartition (SG-TBP) and single anastomosis duodeno-ileal bypass with sleeve gastrectomy (SADI-SG).

To understand the scale of this field, the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) reported in January 2021 that 604,223 primary bariatric procedures are performed worldwide each year, with sleeve gastrectomy remaining the most common. Current international guidelines recommend bariatric surgery for patients with a body mass index (BMI) of 40 kg/m² or higher, or for those with a BMI of 35–40 kg/m² who also have obesity-related health conditions.

This study was designed to answer a simple but important question: What does the future of bariatric surgery research look like? By mapping all upcoming randomized controlled trials, the researchers aimed to clarify which procedures, patient populations, and outcomes will shape the next generation of evidence in this rapidly evolving field.

Study Methods: How the Research Was Conducted

The research team performed a systematic review of registered clinical trials in June 2021 using ClinicalTrials.gov, the world's largest clinical trial registry, which is maintained by the U.S. government and includes safeguards to ensure the validity of registration data.

The search used 2015 Medical Subject Headings (MeSH) from the U.S. National Library of Medicine, with the following key terms: "bariatric surgery," "adjustable gastric banding," "sleeve gastrectomy," "Roux Y gastric bypass," "one anastomosis gastric bypass," "biliopancreatic derivation with switch duodenal," "duodenal switch," "single loop duodeno-jejunal bypass with sleeve gastrectomy," "single anastomosis duodeno-ileal bypass with sleeve gastrectomy," "single anastomosis duodeno-ileal bypass with duodenal switch," and "sleeve gastrectomy with transit bipartition."

The researchers followed the PRISMA statement (a widely accepted guideline for reporting systematic reviews). They included trials that:

• Had not yet been published
• Compared one primary bariatric surgical technique against another surgical procedure or against a medical (non-surgical) treatment
• Enrolled adult patients

There was no restriction on outcomes, meaning the researchers looked at every possible endpoint the trials planned to measure. Two reviewers independently checked each study against the eligibility criteria to ensure accuracy.

For each trial, the team collected details on the comparisons, surgical interventions, geographic location, trial status, planned number of participants, and follow-up duration. They also recorded patient inclusion criteria—including age, BMI, and diabetes status—as well as every predefined primary and secondary outcome.

Outcomes were classified into several categories:

1. Efficacy — weight loss; obesity-related diseases (including hypertension, type 2 diabetes, dyslipidemia, cardiovascular events, cancer, and effects on respiratory, renal, cardiac, liver function, and arthrosis); intermediate metabolic markers (such as glucose homeostasis, beta-cell function, insulin resistance, inflammation, hunger regulation, gut hormones, and gut microbiota); eating behavior; energy expenditure; and health costs.
2. Surgery and perioperative period — associated procedures, length of surgery and anesthesia, hospital stay, conversion to open surgery, pulse rate, grip force testing, oxygen saturation, painkiller use, blood loss, and early complications.
3. Mortality — at various time points after surgery.
4. Complications — divided into medical and surgical complications (with the Dindo–Clavien classification used for surgical complications).
5. Tolerance — quality of life, general satisfaction, and gastrointestinal symptoms.

Data were summarized as percentages for categorical variables and as medians with interquartile ranges for continuous variables. All statistical analyses were performed using R Studio software version 3.3.2.

Key Findings: What the Research Revealed

The Search Results

The electronic search identified 142 references on ClinicalTrials.gov. Of these, 20 were excluded because they were not randomized trials, 38 were duplicates, and 22 were excluded because the results had already been published. This left a final total of 62 randomized controlled trials included in the analysis.

The Trials at a Glance

The 62 upcoming trials plan to enroll a combined total of approximately 10,800 patients. The median number of patients planned per trial is 78 (with half of all trials planning between 50 and 143 participants).

Trial status varied widely:

• 23 trials (37%) were actively recruiting patients
• 12 trials (19%) were completed but not yet published
• 10 trials (16.4%) were active but not recruiting
• 8 trials (13%) were not yet recruiting
• 8 trials (13%) had an unknown status
• 1 trial (1.6%) was terminated

Which Surgical Procedures Are Being Studied

Two procedures dominate the research landscape, each appearing in 39 trials (62.9% of all studies):

• Sleeve gastrectomy (SG) — the most commonly performed bariatric procedure worldwide, in which roughly 80% of the stomach is removed
• Roux-en-Y gastric bypass (RYGB) — a procedure that creates a small stomach pouch and reroutes the small intestine

Other procedures being studied include:

• One anastomosis gastric bypass (OAGBP): 7 trials (11.3%)
• Adjustable gastric banding (AGB): 5 trials (8.1%)
• Single anastomosis duodeno-ileal bypass with sleeve gastrectomy (SADI-SG): 5 trials (8.1%)
• Single loop duodeno-jejunal bypass with sleeve gastrectomy (SLDJBP-SG): 3 trials (4.8%)
• Duodenal switch (DS): 3 trials (4.8%)
• Sleeve gastrectomy with transit bipartition (SG-TBP): 2 trials (3.2%)
• Single anastomosis duodeno-ileal bypass with duodenal switch (SADI-DS): 1 trial (1.6%)
• Biliopancreatic derivation with duodenal switch (BPD-DS): 1 trial (1.6%)
• Nissen sleeve gastrectomy (N-SG): 1 trial (1.6%)

Notably, most trials with very long follow-up periods involve bypass-type procedures: 71% of OAGBP trials plan to follow patients for more than 4 years, as do 40% of SADI-SG trials and all of the SADI-DS, BPD-DS, and DS trials. By contrast, 59% of SG trials follow patients for only 0–1 year.

Where the Trials Are Happening

Half of all upcoming trials (31 trials, 50%) are planned in Europe, making it the most active region for bariatric surgery research. The geographic breakdown is as follows:

• Europe: 31 trials (50%)
• North America: 13 trials (21%)
• Asia: 7 trials (11%)
• South America: 6 trials (9.7%)
• Africa: 5 trials (8.1%)
• Oceania: 0 trials

Interestingly, the emergence of bariatric surgery RCTs in Africa is a notable development, as this region was previously absent from the scientific production of randomized trials in this field.

Who Will Participate in These Trials

The vast majority of trials (94%) plan to enroll adults aged 18 to 70 years. Only 1 trial (1.6%) plans to include older patients aged 65–80, and 3 trials (4.8%) focus on younger adults aged 18–40/50.

Regarding BMI requirements:

• 60% of trials require a BMI of at least 35 kg/m²
• 26% of trials include patients with BMI ≥25/30 kg/m² (overweight to mild obesity)
• 4.8% of trials require BMI ≥40/45 kg/m²
• 3.2% of trials require BMI ≥50 kg/m² (severe obesity)

Nearly a third of trials (29%) focus exclusively on patients with diabetes, highlighting the close relationship between bariatric surgery and metabolic disease management.

How Trials Are Designed: Surgery vs. Medical Treatment

Most trials (63%) use another surgical procedure as the comparison group, while 48% compare surgery against medical (non-surgical) treatment. Some trials use both types of comparators. For example, among RYGB trials, 59% use a medical control group and 59% use a surgical control group.

Follow-up duration is one of the most striking findings:

• 55% of trials follow patients for 1 year or less
• 18% follow patients for 1–2 years
• 4.8% follow patients for 2–3 years
• 0% follow patients for 3–4 years
• 23% follow patients for more than 4 years

What Outcomes Are Being Measured

The most striking shift in bariatric surgery research is the change in focus: weight loss is no longer the most commonly studied outcome. Instead, obesity-related diseases are the most frequent focus, appearing in 80.6% (81%) of all trials.

Among the obesity-related diseases studied:

• Type 2 diabetes: 62.9% of trials
• Dyslipidemia (abnormal blood fats): 45.2% of trials
• Hypertension (high blood pressure): 33.9% of trials
• Respiratory function: 21% of trials
• Liver function: 17.7% of trials

Other outcomes being measured across the trials include:

• Tolerance of surgery (including quality of life, general satisfaction, and gastrointestinal symptoms): evaluated in nearly half of all trials, with quality of life specifically measured in 37%
• Surgical complications — though notably, the standardized Dindo–Clavien classification was used in only 12.9% of trials
• Intermediate metabolic markers (glucose control, beta-cell function, insulin resistance, inflammation, hunger-regulating hormones, gut hormones, and gut microbiota): studied in more than one-third of trials
• Medical complications, including nutritional deficiencies (19.4% of trials), sarcopenia (muscle loss, 3.2%), and mental health (3.2%)
• Mortality and body composition (changes in fat vs. muscle mass)

The growing attention to body composition is particularly important because it helps define undernutrition in recent international guidelines (such as the GLIM criteria).

Clinical Implications: What This Means for Patients

This mapping study offers patients a clear picture of what the future of bariatric surgery may hold. First, the large number of ongoing and upcoming trials reflects the dynamism of this surgical field and the continued commitment to refining surgical techniques.

The shift in focus from weight loss alone to obesity-related diseases and metabolic health is good news for patients. It means future research is increasingly asking whether bariatric surgery can do more than help patients lose weight—it asks whether surgery can improve or even reverse conditions like type 2 diabetes, high blood pressure, abnormal cholesterol, and fatty liver disease. The rise of "metabolic surgery" as a concept supports this broader view of surgery as a treatment for metabolic disease, not just obesity.

However, the short follow-up duration of most trials is a concern. More than half of the trials (55%) plan to follow patients for only 1 year or less, and only 23% extend beyond 4 years. Since bariatric surgery is intended to treat a lifelong chronic disease, the researchers argue that short-term studies may miss important long-term outcomes—both benefits (such as sustained disease remission and improved survival) and risks (including nutritional deficiencies that may take years to develop).

For patients considering bariatric surgery, this means that some of the evidence guiding treatment decisions may be based on relatively short follow-up periods. When discussing surgery with their healthcare team, patients should ask about long-term data for the specific procedure being considered.

Limitations: What This Study Couldn't Tell Us

This study has several limitations that should be kept in mind. First, the review focused only on randomized controlled trials, which provide the highest level of evidence but represent just one part of the broader research landscape. This means the mapping provides a somewhat fragmented view of future bariatric surgery research, since observational studies, registry data, and other study designs were not included.

Second, the researchers note that these registered trials are not guaranteed to be published in the future. Some trials may fail to recruit enough participants, encounter methodological problems, or never reach the publication stage, which could change the actual evidence landscape compared to what the registry predicts.

Finally, information available in clinical trial registries can be incomplete or updated over time. The study reflects a snapshot in time (June 2021), and the status of many trials may have changed since then.

Recommendations: A Roadmap for Future Research

Based on their findings, the researchers make several important recommendations for the future of bariatric surgery research:

1. Extend follow-up durations. Given that bariatric surgery treats a lifelong chronic disease, trials that follow patients for only a few months or a single year are insufficient. Future trials should be designed with longer follow-up periods—ideally 4 years or more—to capture the full range of benefits and risks.
2. Invest more in under-researched areas. Nutritional deficiency risk, sarcopenia (muscle wasting), and mental health after surgery remain severely underinvestigated, with only 3.2% of trials studying the latter two. Given the potential consequences of nutritional deficiencies and the concerning rates of depressive syndrome or addiction after bariatric surgery, these areas deserve greater attention.
3. Standardize how complications are reported. Only 12.9% of trials used the standardized Dindo–Clavien classification for surgical complications. Consistent use of validated classification systems would make it easier to compare results across studies.
4. Support research in underrepresented regions. The emergence of trials in Africa is promising, but the global distribution of research remains uneven, with Europe and North America dominating the field. Wider geographic diversity would improve the generalizability of findings to patients worldwide.
5. Avoid research waste. By carefully considering what is already known and addressing questions that have not yet been answered, future studies can avoid duplicating existing evidence and focus resources on the most meaningful questions.

For patients, this roadmap reinforces the importance of asking their surgical team about the long-term evidence base for any procedure, including data on quality of life, nutritional outcomes, and mental health support after surgery.

Frequently Asked Questions

Who is eligible for bariatric surgery based on current international guidelines?

Current guidelines recommend bariatric surgery for adults with a body mass index (BMI) of 40 kg/m² or higher, or for those with a BMI of 35 to 40 kg/m² who also have obesity-related health conditions. Eligibility should always be confirmed by a qualified healthcare team. The procedure requires a lifelong commitment to nutritional follow-up.

Which bariatric procedures are most often studied in upcoming clinical trials?

Sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB) are the most-studied procedures, each appearing in 39 of the 62 upcoming randomized controlled trials. Other techniques studied include one anastomosis gastric bypass, adjustable gastric banding, and SADI-SG. These trials plan to enroll about 10,800 patients in total.

How long do most upcoming bariatric surgery trials follow patients after surgery?

More than half of the upcoming trials (55%) follow patients for one year or less. Only about 23% extend beyond four years. Researchers consider this too short for a lifelong condition like obesity, because important benefits and risks, such as nutritional deficiencies, may take years to appear. Patients should ask about long-term data.

What is the main focus of new bariatric surgery research?

Obesity-related diseases have overtaken weight loss as the most common focus. Type 2 diabetes appears in 62.9% of trials, dyslipidemia in 45.2%, and hypertension in 33.9%. This shift supports the concept of metabolic surgery, meaning future research asks whether surgery can improve or reverse conditions like diabetes, not just produce weight loss.

Where in the world are the upcoming bariatric surgery trials being conducted?

Half of all upcoming trials (31 of 62) are planned in Europe, making it the most active region. North America accounts for 21%, Asia 11%, South America about 10%, and Africa 8%. The emergence of trials in Africa is notable because this region previously had no randomized bariatric surgery trials, according to the mapping study.

What should I ask my surgical team about long-term evidence for a weight-loss procedure?

Ask about long-term data for the specific procedure you are considering, including follow-up beyond one year. Also ask about quality of life, nutritional outcomes, and mental health support after surgery. The researchers recommend future trials focus on nutritional deficiencies, muscle loss, and mental health because these areas remain underinvestigated in current research.

What limitations of this study should patients be aware of?

The study included only randomized controlled trials, not observational studies or registries. It is a snapshot from June 2021, so trial statuses may have changed. Also, registered trials are not guaranteed to be published later; some may fail to recruit enough participants or encounter other problems. Therefore, the actual future evidence may differ from this map.

Source Information

Original article title: The future of bariatric surgery research A worldwide mapping of registered trials

Authors: Claire Rives-Lange, Tigran Poghosyan, Nathalie Rassy, Claire Carette, Aurelie Phan, Marc Goeau-Brissonnière, Flore de Castelbajac, Amel Merazka, and Sebastien Czernichow

Journal: Obesity Reviews, 2022;23:e13433. Published by the World Obesity Federation (Wiley).

DOI: 10.1111/obr.13433

Funding: This study was conducted without funding.

Disclosures: The authors declared the following potential conflicts of interest: Sebastien Czernichow received consulting fees from Novonordisk, Lilly, Fresenius Kabi, Janssen, Novartis, Servier, and Boehringer; participated on Data Safety Monitoring Boards for Bariatek and Novonordisk; and holds stock or stock options in Jellynov and Mygoodlife. Claire Carette received consulting fees from AstraZeneca, Lilly, Novartis Pharma, MSD France, IPSEN Pharma, Pfizer, and Publicis Health, and received travel support from Astra Zeneca, Novo Nordisk, Lilly, Vitalaire, and MSD France. All other authors declared no conflicts of interest.

This patient-friendly article is based on peer-reviewed research. It is intended for educational purposes and does not constitute medical advice. Patients considering bariatric surgery should consult with qualified healthcare professionals.