Time-Restricted Eating After Bariatric Surgery

June 26, 2026 updated by: Seher Şen, Medipol University

Comparison of Time-Restricted Intermittent Fasting Diet in Individuals With and Without Bariatric Surgery

This study aims to compare the effects of time-restricted eating (TRE, 16/8) in adults with obesity who have and have not undergone bariatric surgery (BS). The study will include adults aged 18-65 years: those with obesity who have not undergone BS, and those who have experienced insufficient weight loss (IWL) or weight regain (WR) following BS. Both groups will follow a 16:8 time-restricted eating protocol for 6 weeks, with an 8-hour eating window recommended between 10:00 AM and 6:00 PM, though participants may adjust to other 16-hour fasting windows. Participants will be evaluated before and after the intervention in terms of anthropometric measurements, biochemical parameters, and dietary habits. The study is being conducted at a private hospital in Bursa, Turkey, and is planned to be completed with a total of 40 participants (20 per group).

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Detailed Description

Obesity remains a major global health concern, with bariatric surgery (BS) being the most effective treatment for severe obesity. However, some patients experience insufficient weight loss (IWL) or weight regain (WR) approximately 18 months after surgery, which is associated with recurrence of obesity-related comorbidities and reduced quality of life.

Time-restricted eating (TRE), a form of intermittent fasting, has emerged as a promising dietary approach for obesity management. The 16/8 TRE model, which limits food intake to an 8-hour window, has shown beneficial effects on body weight, insulin resistance, glycemic control, and lipid profiles in non-surgical individuals with obesity. However, evidence regarding its efficacy and safety in post-bariatric surgery patients remains limited.

This prospective controlled study will enroll 40 adults with obesity (20 per group): Group 1 - adults with obesity who have not undergone BS; Group 2 - adults with IWL or WR following BS. All participants will follow a 16:8 TRE protocol for 6 weeks, with nutritional principles aligned with ASMBS guidelines. Follow-up visits will be conducted face-to-face at baseline, day 15, day 30, and day 45, with additional weekly contact via phone or WhatsApp. Anthropometric measurements will be assessed at baseline and at week 6. Dietary intake will be evaluated using 3-day food records and food frequency questionnaires, analyzed with the BEBİS-9 nutrition software.

Study Type

Interventional

Enrollment (Estimated)

40

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Locations

  • Turkey (Türkiye)
      • Bursa, Turkey (Türkiye), 16940
        • Recruiting
        • Nev Sağlık Grubu
        • Contact:
          • Nev Sağlık Grubu dallı Seher ŞEN, Assistant Professor
          • Phone Number: 05393919700
          • Email: seherdalli@gmail.com
    • Lütfen Seçiniz.

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • Adults aged 18-65 years with obesity who have not undergone bariatric surgery
  • Adults aged 18-65 years with obesity who have undergone bariatric surgery and experienced insufficient weight loss (IWL) within 18 months post-surgery, -defined as %EWL <50% at 18 months
  • Adults aged 18-65 years with obesity who have undergone bariatric surgery and experienced weight regain (WR), defined as >25% increase in %EWL from the lowest recorded weight

Exclusion Criteria:

  • Pregnant or breastfeeding individuals
  • Acute illness, active infection, or comorbid conditions limiting treatment efficacy and safety, including: cancer, type 1 diabetes, renal or hepatic failure, recent stroke or myocardial infarction, nephrolithiasis, drug or alcohol abuse, eating disorders, severe depression or other psychiatric disorders, inflammatory bowel disease (IBD), neoplasia, arrhythmic heart disease, heart failure, respiratory failure, or corticosteroid therapy
  • Professional athletes

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Non-Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Active Comparator: Arm 1: Adults with Obesity (Non-Bariatric)
Adults with obesity who have not undergone bariatric surgery. Will follow 16:8 TRE protocol for 6 weeks.
Behavioral: Time-Restricted Eating (16:8)
Participants will follow a 16:8 time-restricted eating protocol for 6 weeks, limiting food intake to an 8-hour window (recommended 10:00 AM-6:00 PM, with flexibility to adjust). During the 16-hour fasting period, only water and non-caloric beverages (tea, coffee, soda) are permitted. Nutritional principles will be aligned with ASMBS guidelines.
Other Names:
  • 16/8 Fasting
Experimental: Arm 2: Adults with Obesity (Post-Bariatric)
Adults with obesity who experienced insufficient weight loss or weight regain following bariatric surgery. Will follow 16:8 TRE protocol for 6 weeks.
Behavioral: Time-Restricted Eating (16:8)
Participants will follow a 16:8 time-restricted eating protocol for 6 weeks, limiting food intake to an 8-hour window (recommended 10:00 AM-6:00 PM, with flexibility to adjust). During the 16-hour fasting period, only water and non-caloric beverages (tea, coffee, soda) are permitted. Nutritional principles will be aligned with ASMBS guidelines.
Other Names:
  • 16/8 Fasting

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Body Weight
Time Frame: Baseline and 6 weeks
Change in body weight measured by digital scale
Baseline and 6 weeks
Body Mass Index (BMI)
Time Frame: Baseline and 6 weeks
Change in BMI calculated as weight (kg) divided by height squared (m²)
Baseline and 6 weeks
Body Fat Mass
Time Frame: Baseline and 6 weeks
Change in fat mass assessed by bioelectrical impedance analysis (Tanita MC-780 MA)
Baseline and 6 weeks
Muscle Mass
Time Frame: Baseline and 6 weeks
Change in muscle mass assessed by bioelectrical impedance analysis (Tanita MC-780 MA)
Baseline and 6 weeks
Waist Circumference
Time Frame: Baseline and 6 weeks
Change in waist circumference measured at 5 cm below the navel
Baseline and 6 weeks
Hip Circumference
Time Frame: Baseline and 6 weeks
Change in hip circumference measured at the maximum point of gluteal muscles
Baseline and 6 weeks
Percentage of Excess Weight Loss (%EWL)
Time Frame: Baseline and 6 weeks
Calculated as: [(preoperative weight - postoperative weight) / (preoperative weight - ideal weight)] × 100. Ideal body weight defined based on a BMI of 25 kg/m². Insufficient weight loss (IWL) defined as
Baseline and 6 weeks
Percentage of Total Weight Loss (%TWL)
Time Frame: Baseline and 6 weeks
Calculated as: [(preoperative weight - postoperative weight) / preoperative weight] × 100. Used to assess overall weight loss outcomes in both bariatric and non-bariatric participants following the 6-week time-restricted eating intervention.
Baseline and 6 weeks

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Daily Energy Intake
Time Frame: Baseline and 6 weeks
Change in daily energy intake (kcal/day) assessed by 3-day dietary records (including one weekend day) and food frequency questionnaire, analyzed using the Nutritional Information System software (BEBİS-9). Data collected through face-to-face interviews at baseline and week 6.
Baseline and 6 weeks
Dietary Macronutrient Distribution
Time Frame: Baseline and 6 weeks
Change in daily macronutrient intake including carbohydrate (%), protein (%), and fat (%) assessed by 3-day dietary records and food frequency questionnaire, analyzed using BEBİS-9 software. Target distribution for post-bariatric participants: carbohydrate 48-55%, protein 23-27%, fat 21-27% of total daily energy intake, in accordance with ASMBS guidelines.
Baseline and 6 weeks

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Medipol University

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

July 12, 2025

Primary Completion (Estimated)

June 1, 2026

Study Completion (Estimated)

July 12, 2026

Study Registration Dates

First Submitted

June 23, 2026

First Submitted That Met QC Criteria

June 26, 2026

First Posted (Actual)

June 29, 2026

Study Record Updates

Last Update Posted (Actual)

June 29, 2026

Last Update Submitted That Met QC Criteria

June 26, 2026

Last Verified

June 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • MUDU-SBE-SS-04

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 participant confidentiality and institutional data privacy regulations.

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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