One-Year Outcomes After Conversion Bariatric Surgery

ONE-YEAR OUTCOMES OF ANTHROPOMETRIC, BIOCHEMICAL, AND NUTRITIONAL PARAMETERS AFTER CONVERSION BARIATRIC SURGERY

Obesity is a growing global public health problem, and bariatric surgery is currently the most effective treatment for achieving sustained weight loss and improving obesity-related comorbidities. However, a subset of patients experience inadequate weight loss or weight regain following primary bariatric surgery, which may lead to the recurrence of metabolic complications and reduced quality of life. In such cases, conversion bariatric surgery, defined as the surgical conversion from one bariatric procedure to another, is considered an important therapeutic option. Despite the increasing number of conversion procedures, comprehensive longitudinal data evaluating anthropometric, biochemical, and nutritional outcomes after conversion bariatric surgery remain limited.

This study aims to prospectively evaluate individuals undergoing conversion bariatric surgery due to weight regain following primary bariatric surgery. Anthropometric measurements, biochemical parameters, and nutritional status will be assessed preoperatively and at 1 year after surgery. By evaluating weight loss outcomes together with metabolic and nutritional changes, this study seeks to provide clinically relevant evidence to guide postoperative follow-up strategies, optimize nutritional management, and support multidisciplinary care in patients undergoing conversion bariatric surgery.

Study Overview

• Status: Active, not recruiting
• Conditions: Bariatric Surgery; Revisional Bariatric Surgery; Obesity & Overweight

• Study Type: Observational
• Enrollment (Estimated): 14

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Bursa
    • Osmangazi, Bursa, Turkey (Türkiye), 16160
      • Mudanya Univesity

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Adult patients aged 18-65 years who had previously undergone bariatric surgery and subsequently received conversion bariatric surgery due to suboptimal clinical response, defined as suboptimal weight loss or recurrent weight gain. Participants are followed in routine clinical practice and evaluated preoperatively and at postoperative 1 year for anthropometric, biochemical, nutritional, and physical activity outcomes.

Description

Inclusion Criteria:

• Adults aged 18-45 years
• Previously underwent bariatric surgery
• Subsequently underwent conversion bariatric surgery due to suboptimal clinical response

Suboptimal clinical response defined as either:

• Suboptimal Clinical Response (SCR): maximum total weight loss (TWL%) of <20% within 18 months after metabolic and bariatric surgery
• Recurrent Weight Gain (RWG): regaining >30% of initial postoperative weight loss after achieving initial weight reduction

Exclusion Criteria:

• Pregnancy or lactation
• Presence of acute illness or infection
• Comorbid conditions that could limit treatment efficacy or compromise safety
• Participation in professional athletic activity

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort
Conversion Bariatric Surgery; This cohort includes patients who previously underwent conversion bariatric surgery as part of routine clinical care and were followed observationally. Anthropometric measurements, biochemical parameters, and nutritional status were assessed at the preoperative period and postoperative month 12 (1 year).

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Body Composition Parameters	Body composition parameters including fat mass, fat percentage, fat-free mass, fat-free mass percentage, skeletal muscle mass, muscle percentage, and extracellular water to total body water ratio assessed using multi-frequency bioelectrical impedance analysis (BIA).	Preoperative baseline and postoperative 1 year
Change in Body Weight	Change in body weight (kg) measured using a digital scale with participants wearing light clothing and no shoes.	Preoperative baseline and postoperative 1 year
Change in Body Mass Index (BMI)	Change in body mass index (kg/m²) calculated from measured body weight and height.	Preoperative baseline and postoperative 1 year
Percentage of Total Weight Loss	Percentage of total weight loss calculated as [(preoperative weight - postoperative weight) / preoperative weight] × 100.	postoperative 1 year
Percentage of Excess Weight Loss	Percentage of excess weight loss calculated as [(preoperative weight - postoperative weight) / (preoperative weight - ideal body weight)] × 100, with ideal body weight defined as a BMI of 25 kg/m².	postoperative 1 year
Change in Waist Circumference	Waist circumference (cm) measured in the standing position using a non-elastic measuring tape at the midpoint between the lowest rib and the iliac crest.	Preoperative baseline and postoperative 1 year
Change in Hip Circumference	Hip circumference (cm) measured in the standing position at the point of maximum protrusion of the gluteal muscles using a non-elastic measuring tape.	Preoperative baseline and postoperative 1 year
Change in Body Fat Percentage (%)	Body fat percentage measured using multi-frequency bioelectrical impedance analysis (BIA).	Preoperative baseline and postoperative 1 year
Change in Fat-Free Mass (kg)	Fat-free mass measured using multi-frequency bioelectrical impedance analysis (BIA).	Preoperative baseline and postoperative 1 year
Change in Skeletal Muscle Mass (kg)	Skeletal muscle mass measured using multi-frequency bioelectrical impedance analysis (BIA).	Preoperative baseline and postoperative 1 year

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Fasting Plasma Glucose	Changes in fasting plasma glucose levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in Alanine Aminotransferase (ALT)	Changes in alanine aminotransferase (ALT) levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in Hematological Parameters	Changes in hemoglobin and hematocrit levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in Iron Status Parameters	Changes in serum ferritin, serum iron, and total iron-binding capacity levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in Micronutrient and Electrolyte Levels	Changes in serum vitamin B12, folic acid, magnesium, total calcium, sodium, and potassium levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in Fasting Insulin	Changes in fasting insulin levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in Glycated Hemoglobin (HbA1c)	Changes in glycated hemoglobin (HbA1c) levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in Total Cholesterol	Changes in total cholesterol levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in LDL Cholesterol	Changes in low-density lipoprotein (LDL) cholesterol levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in HDL Cholesterol	Changes in high-density lipoprotein (HDL) cholesterol levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in Triglyceride Levels	Changes in triglyceride levels measured from venous blood samples	Preoperative baseline and postoperative 1 year
Change in Aspartate Aminotransferase (AST)	Changes in aspartate aminotransferase (AST) levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in Urea Levels	Changes in serum urea levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year
Change in Uric Acid Levels	Changes in serum uric acid levels measured from venous blood samples.	Preoperative baseline and postoperative 1 year

Collaborators and Investigators

• Sponsor: Medipol University
• Collaborators: Mudanya University
• Investigators: Principal Investigator: Seher Şen, Assistant Professor, Mudanya University

Study record dates

Study Major Dates

• Study Start (Actual): November 12, 2024
• Primary Completion (Actual): January 10, 2026
• Study Completion (Estimated): February 21, 2026

Study Registration Dates

• First Submitted: December 17, 2025
• First Submitted That Met QC Criteria: January 8, 2026
• First Posted (Actual): January 15, 2026

Study Record Updates

• Last Update Posted (Actual): February 3, 2026
• Last Update Submitted That Met QC Criteria: February 2, 2026
• Last Verified: February 1, 2026

More Information

Terms related to this study

• Keywords: obesity; anthropometric measurements; nutritional assessment; weight regain; metabolic outcomes; conversion bariatric surgery
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Overweight; Obesity
• Other Study ID Numbers: MUDU-SBE-SS-01

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will not be shared due to the need to protect patient privacy and confidentiality.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No