24-hour Clear Liquid Diet vs. Standard Fasting for Upper Gastrointestinal Endoscopy in Patients Taking Agonists of the GLP-1 Receptor (CLEAR-GLP1)

November 5, 2026 updated by: Rita Regatia, Portuguese Oncology Institute, Coimbra

24-hour Clear Liquid Diet vs. Standard Fasting for Upper Gastrointestinal Endoscopy in Patients Taking Agonists of the GLP-1 Receptor (CLEAR-GLP1 Trial): a Randomized, Parallel-group, Multicentre, International Clinical Trial

GLP-1 receptor agonists delay gastric emptying and are associated with a higher rate of retained gastric content (RGC) during upper gastrointestinal endoscopy, even under standard fasting. No randomized trial has compared fasting strategies in this population. CLEAR-GLP1 is a multicentre, international, investigator-blinded randomized trial comparing a 24-hour clear liquid diet (followed by a 2-hour fast) with standard fasting (6 hours for solids, 2 hours for clear liquids) in adults on GLP-1 RA therapy undergoing elective upper endoscopy. GLP-1 RA therapy is not interrupted in either arm. The primary outcome is the rate of clinically significant RGC, defined as a GRACE stomach score of 0.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

The primary objective of the study it to determine whether a 24-hour clear liquid diet protocol reduces the incidence of retained gastric content compared with a standard fasting protocol, graded endoscopically using a validated visibility scale (stomach GRACE score=0 vs. stomach GRACE scores=1, 2 or 3), in patients on GLP-1 receptor agonist therapy undergoing elective UGI endoscopy.

Study Type

Interventional

Enrollment (Estimated)

250

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

  • Portugal
      • Coimbra, Portugal, 3030-508
        • Portuguese Oncology Institute of Coimbra
        • Contact:

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

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

All

Description

Inclusion Criteria:

  • Age ≥ 18 years;
  • Current treatment with a GLP-1 receptor agonist for at least 4 weeks, regardless of indication;
  • Referral for elective upper gastrointestinal endoscopy (isolated or combined with colonoscopy);
  • Informed consent for both the upper gastrointestinal endoscopy procedure and study participation.

Exclusion Criteria:

  • Urgent/emergency endoscopy;
  • Previously diagnosed gastroparesis;
  • Prior major gastric/esophageal surgery (e.g., gastrectomy, gastric bypass);
  • Known or suspected upper gastrointestinal obstruction;
  • Pregnancy;
  • Refusal or inability to comply with the assigned fasting protocol.

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: Prevention
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Double

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: 24-Hour Clear Liquid Diet

24-hour clear liquid diet: exclusively clear liquids for the 24 hours preceding the upper gastrointestinal endoscopy, with a 2-hour complete fast, including for liquids
Other: 24-Hour Clear Liquid Diet

24-hour clear liquid diet prior to upper gastrointestinal endoscopy with a 2-hour complete fast, including for liquids
Active Comparator: Standard Fasting

Standard pre-procedural fasting according to current recommendations: the patient keeps a standard fasting prior to the upper gastrointestinal endoscopy, with a 6-hour fast for solid food and 2-hour fast for liquids
Other: Standard Fasting

Standard fasting prior to upper gastrointestinal endoscopy, of 6-hours for solid foods and 2 hours for liquids

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Incidence of Retained Gastric Content
Time Frame: During the index upper gastrointestinal endoscopy (Day 0)

Proportion of patients with clinically significant retained gastric content, defined as a GRACE (Gastroscopy RAte of Cleanliness Evaluation) stomach score of 0 (solid food precluding visualization of the underlying mucosa), compared with GRACE stomach scores of 1, 2 or 3. The GRACE stomach score ranges from 0 to 3; higher scores indicate better mucosal cleanliness.
During the index upper gastrointestinal endoscopy (Day 0)

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Procedure interruption rate due to retained gastric content and risk of aspiration
Time Frame: Day 0
Day 0
Peri-procedural adverse events (aspiration, SpO₂ <90%, emergent advanced airway)
Time Frame: Day 0
Day 0
Inadequate visualization rate (GRACE stomach 0-1 vs 2-3)
Time Frame: Day 0

Percentage of participants with a Gastroscopy RAte of Cleanliness Evaluation (GRACE) stomach score of 0 or 1, compared with scores of 2 or 3. The GRACE stomach score ranges from 0 to 3; higher scores indicate better mucosal cleanliness.
Day 0
Optimal visualization rate (GRACE stomach 3 vs 0-2)
Time Frame: Day 0

Percentage of participants with a Gastroscopy RAte of Cleanliness Evaluation (GRACE) stomach score of 3, compared with scores of 0, 1 or 2. The GRACE stomach score ranges from 0 to 3; higher scores indicate better mucosal cleanliness.
Day 0
Gastric lesion detection rate
Time Frame: Up to 4 weeks

Gastric lesion detection rate defined as the detection of any subepithelial lesion, extensive intestinal metaplasia, dysplasia, carcinoma, neuroendocrine tumour, or lymphoma.
Up to 4 weeks
Peri-procedural hypoglycemia (capillary glucose <70 mg/dL), before and after the procedure
Time Frame: Day 0
Day 0

Other Outcome Measures

Outcome Measure
Measure Description
Time Frame
Total GRACE score
Time Frame: Day 0

Gastroscopy RAte of Cleanliness Evaluation (GRACE) Total Score Sum of the esophagus, stomach and duodenum GRACE scores; Range 0 to 9; higher scores indicate better mucosal cleanliness.
Day 0
GRACE esophagus score
Time Frame: Day 0

Gastroscopy RAte of Cleanliness Evaluation (GRACE) Esophagus Score; Range 0 to 3; higher scores indicate better mucosal cleanliness.
Day 0
GRACE stomach score
Time Frame: Day 0

Gastroscopy RAte of Cleanliness Evaluation (GRACE) Stomach Score; Range 0 to 3; higher scores indicate better mucosal cleanliness.
Day 0
GRACE duodenum score
Time Frame: Day 0

Gastroscopy RAte of Cleanliness Evaluation (GRACE) Duodenum Score; Range 0 to 3; higher scores indicate better mucosal cleanliness
Day 0

Collaborators and Investigators

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

Sponsor

Portuguese Oncology Institute, Coimbra

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

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 (Estimated)

January 1, 2027

Primary Completion (Estimated)

December 1, 2027

Study Completion (Estimated)

December 1, 2027

Study Registration Dates

First Submitted

November 2, 2026

First Submitted That Met QC Criteria

November 5, 2026

First Posted (Actual)

November 10, 2026

Study Record Updates

Last Update Posted (Actual)

November 10, 2026

Last Update Submitted That Met QC Criteria

November 5, 2026

Last Verified

November 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • CLEAR-GLP1

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

De-identified individual participant data underlying the results reported in the primary publication (baseline characteristics, fasting arm, GLP-1 RA type and dose, time since last dose, GRACE scores, adverse events and lesion detection) will be shared, in compliance with the General Data Protection Regulation (GDPR).

IPD Sharing Time Frame

Beginning 9 months and ending 36 months after publication of the primary results.

IPD Sharing Access Criteria

Researchers who provide a methodologically sound proposal, approved by the principal investigator. Proposals should be directed by email. To gain access, data requestors will need to sign a data access agreement.

IPD Sharing Supporting Information Type

  • STUDY_PROTOCOL
  • SAP
  • ICF

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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