Morbid Obesity Requiring Bariatric SurgeryFLAGNCT07565051
Can Pre-operative Lean Mass Predict Weight Loss After Roux-en-Y Gastric Bypass?
An observational study of Morbid Obesity Requiring Bariatric Surgery, run by University Hospital, Geneva at 1 site in Switzerland.
Trial summary
The goal of this observational study is to evaluate whether preoperative fat-free mass predicts post-operative weight loss in patients undergoing Roux-En-Y gastric bypass. The primary objective of this study is to evaluate whether preoperative fat-free mass predicts weight loss in the two years following RYGB. Read more about this study
- Who is it for?
- Any age
- Conditions the study is for
- Morbid Obesity Requiring Bariatric Surgery
- How many people
- 91 participants
- Where
- 1 siteSwitzerland
- Study dates
- 18 Aug 2025to 18 Aug 2032
- How long will I take part?
- 5 Years
- Phase
- Observational
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages Any age
- All sexes
- No healthy volunteers
- Child, Adult, Older adult
Study population: Patients with scheduled gastric bypass at the Geneva University Hospitals (HUG)
Who may be able to join
- Patients ≥ 18 years AND
- Meeting inclusion criteria for RYGB (www.smob.ch): BMI ≥35 kg/m2, failure of weight-reducing programs over 2 years (for patients with a BMI ≥50 kg/m2, 1 year), understanding of the necessity to change the lifestyle and eating habits post-operatively, signed consent for lifelong post-operative follow-up in a recognized bariatric center AND
- Scheduled RYGB at the HUG OR previous RYGB at the HUG with a present follow-up in Clinical Nutrition and dietetics at the HUG AND
- Understanding French
Who cannot join
- Inability or refusal to give consent.
- Planification for another type of bariatric surgery than RYGB
- Contra-indications to bariatric surgery as stated under www.smob.ch: insufficient nutritional knowledge in nutrition to lose weight, pregnancy, kidney failure (Creatinine ≥ 300 umol/l without dialysis, Crohn's disease, active cancer or remission < 2 years, active psychiatric disease, substance abuse (alcohol, cannabis, opioids), absence of compliance, lack of understanding of the requirements and necessary lifestyle changes reported by physician or dietician.
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
Switzerland1 site, 1 recruiting
- Recruiting
Geneva University Hospitals
Geneva, Canton of Geneva, 1205
About this study
The goal of this observational study is to evaluate whether preoperative fat-free mass predicts post-operative weight loss in patients undergoing Roux-En-Y gastric bypass. The primary objective of this study is to evaluate whether preoperative fat-free mass predicts weight loss in the two years following RYGB.
The investigators will collect the following data, assessed as part of routine follow-up:
Read more
- height, weight, hip and waist circumferences
- body composition by bioimpedance analysis and dual energy-X-ray absorptiometry
- Muscle strength and physical activity
- Nutritional parameters: resting energy expenditure, eating behavior and digestive tolerance", plasma micronutrient status. .
- Cardiovascular risk factors: fasting glucose, blood levels of Hb1Ac, triglycerides, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, blood pressure
- Co-morbidities: joint pain and arthritis, sleep apnea, gastro-oesophageal reflux, metabolic dysfunction-associated fatty liver disease (MAFLD), cancer, stroke, heart attack.
Quality of life: quality of life by the "Bariatric Analysis and Reporting Outcome (BAROS) questionnaire", symptoms of dumping syndrome by the "Sigstad diagnostic score system" Birthdate, birthweight and term of their children
Read the detailed description
This study is prospective but the investigators will also use the retrospective data of the patients who underwent bariatric surgery before the acceptance of the study, with their informed consent.
The investigators will collect the following data, assessed as part of routine follow-up:
Preoperatively:
- medical history
- height, weight, hip and waist circumferences
- body composition by bioimpedance analysis (BIA) and dual energy-X-ray absorptiometry (DXA)
- handgrip strength
- sarcopenia questionnaire (SARC-F)
- physical activity questionnaire (IPAQ)
- resting energy expenditure by indirect calorimetry
- eating behaviour: duration of meals, hyperphagia, snacking, compulsions, and cognitive restrictions as variables dichotomized as yes or no, and hunger and satiety each through a visual analogue scale, where 0 corresponds to "no hunger or good satiety" and 10 to "big hunger or no satiety"
- digestion symptoms: frequency of vomiting and of bowel movements
- Binge eating questionnaire
- blood pressure
- blood sample
- co-morbidities
- results of liver ultrasound, gastric endoscopy
- quality of life questionnaire (BAROS), Dumping questionnaire (Sigstad)
- blood and tissue biobanking
These assessments will be repeated after surgery at the frequency indicated below:
- at month 1: all tests except DXA, sarcopenia questionnaire (SARC-F), physical activty assessment (IPAC), binge eating questionnaire, liver ultrasound and gastric endoscopy, quality of life and dumping questionnaire, blood and tissue biobank
- At month 3: all tests except DXA, binge eating questionnaire, dumping, questionnaire, and only if indicated for clinical routine, liver ultrasound and gastric endoscopy.
- At month 6: all tests except DXA, sarcopenia questionnaire (SARC-F), physical activty assessment (IPAC), binge eating questionnaire, quality of life questionnaire, and only if indicated for clinical routine, liver ultrasound and gastric endoscopy, only if indicated in clinical routine, blood and tissue biobank.
- At year 1, 2, 3, 4 and 5: all tests except liver ultrasound and gastric endoscopy only if indicated in clinical routine
- At year 1.5: all tests except DXA, sarcopenia questionnaire (SARC-F), blood and tissue biobank
Study sample calculation:
The investigators hypothesized, in a conservative way and based on available litterature, that the patients will decrease their lean mass by 5±10 kg within 2 years after RYGB. A sample size of 32 achieves 90% power to detect a mean of paired differences of 5 kg with an estimated standard deviation of paired differences of 10.0 and with a significance level (alpha) of 0.050 using a two-sided paired t-test.
The investigators plan to evaluate whether preoperative FFM (independent variable) predicts weight loss (dependent variable) while adjusting for age, sex, preoperative BMI category (35-40, 40-50, > 50), and FM, physical activity. This corresponds to 6 adjustment variables altogether, or 3 supplemental variables. According to the rule of Harrel that stipulates at least 10 observations per independent variables, the investigators need at least 70 participants (10*(1+6)) to perform these adjustments.
Considering a drop-out rate of 30% at 2 years, the investigators will need a sample size of: 70+30% = 91 subjects.
- Keywords
- obesity, gastric bypass, body composition, bone mineral density, handgrip strength, sarcopenic obesity
- Medical subject headings
- Obesity
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
| Study group | Role | What they receive |
|---|---|---|
| Patients with scheduled RYGB at the Geneva University Hospitals | Morbidly obese patients scheduled for Roux-en-Y gastric bypass |
What is being measured
The primary outcome is the main question the study is designed to answer.
Correlation between Fat-free mass (FFM) and weight loss following RYGB
FFM and lean body mass measurement using BIA and DXA, respectively
Measured: 2 years
Evolution of body composition in the two years after bariatric surgery
Measurments of body composition by dual energy X-ray absorptiometry before gastric bypass and yearly after gastric bypass
Measured: 5 years
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted4 May 2026
- Study start18 Aug 2025
- Primary completion18 Aug 2027 (estimated)
- Study completion18 Aug 2032 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Morbid Obesity Requiring Bariatric SurgeryStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Observational
- Observational model
- Cohort
- Time perspective
- Other
- Enrolment
- 91 participants (estimated)
- Target duration
- 5 Years
Sponsor and investigators
- Lead sponsor
- University Hospital, Geneva
- Sponsor type
- University, hospital or other
- Responsible party
- Principal investigator, Genton Graf Laurence, University Hospital, Geneva
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07565051
- Sponsor's protocol ID
- 2024-02136
- Acronym
- FLAG
- Status last verified
- Apr 2026
- First submitted
- 27 Apr 2026
- Last updated
- 8 May 2026
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No