The Effect of Fasting on Peak Fat Oxidation, Mitochondrial Coupling and Extracellular Matrix (GlycoFast84)

July 2, 2026 updated by: Jørn Wulff Helge, University of Copenhagen

The Effect of Fasting on Peak Fat Oxidation, Mitochondrial Coupling and Extracellular Matrix in Healthy Men and Lean and Obese Men and Women

The interventional study will recruit four groups (n=10 per group): Young men and women with normal weight (BMI 18-25), and young men and women with obesity (BMI >30). The study will investigate the effect of 84 hours of fasting on peak fat oxidation, mitochondrial coupling and the extracellular matrix.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Detailed Description

Four groups of young normal weight men (n=10) and women (n=10) and young obese men (n=10) and women (10) are recruited. After verbal and written information is provided signed consent is obtained.

Prior to the first day of the trial, the participants must complete a four-day dietary and exercise record based on the weighing of all food and beverages consumed and tracking all exercise. This is used to asses the participant's habitual diet and activity level. For female participants, an additional form must be completed regarding their menstrual cycle and form of contraception.

On the two trial days (before and after fasting), participants arrive at the laboratory in the morning, and on the first day, the participant will have fasted since the previous evening. Furthermore, participants have been asked to minimize strenous physical activity for 24 hours leading up to testing. Prior to day 1, participants have been instructed to consume a habitual carbohydrate-rich diet for the 48 hours preceding the first test day.

Initially, the participants' body composition is determined by DXA, after which the participants rest for 15 minutes. Subsequently, blood pressure is measured in the supine position whereafter resting energy expenditure is measured by indirect calorimetry. A venous blood sample is taken from the antecubital vein, as well as a biopsy from the m. vastus lateralis and from the subcutaneous abdominal adipose tissue using the Bergström technique applied with suction. After 30 minutes of rest, a graded exercise test on a cycle ergometer is initiated to determine peak fat oxidation and maximal oxygen uptake. After the test is completed and following a minimum of 10 minutes of rest, handgrip strength and knee extension strength are measured. This concludes the test day.

Thereafter, the 84-hour fast is initiated. During the fasting period, the subjects will communicate by telephone each morning with one of the researchers regarding their well-being and any questions they may have. On day 2 subjects will do 1 hour of submaximal exercise. During the fasting subjects will be provided with electrolyte tablets. Following the 84 hours, the subjects return to the laboratory. Here, the same protocol as described above is carried out. This concludes the test day and the experiment.

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

  • Denmark
      • Copenhagen, Denmark, 2200
        • Recruiting
        • Department of Biomedical Sciences
        • 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

  • Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Healthy normal weight men aged [18,40] and BMI [18,25]
  • Healthy normal weight women [18,40] and BMI [18,25]
  • Healthy obese men [18,40] and BMI [30,40]
  • Healthy obese women [18,40] and BMI [30,40]

Exclusion Criteria:

  • Present or former cardiovascular disease and chronical inflammatory disease
  • Consumption of medications and supplements that influence substrate use at rest and/or during exercise
  • Pregnancy

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: Basic Science
  • Allocation: Non-Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Young normal weight men
BMI [18, 25] Age [18, 40]
Other: Diet
Long-term fasting (84 hours), physiological testing before and after fasting: sampling of blood, abdominal adipose tissue and skeletal muscle for molecular analysis and respiratory measurements at rest.
Experimental: Young normal weight women
BMI [18, 25] Age [18, 40]
Other: Diet
Long-term fasting (84 hours), physiological testing before and after fasting: sampling of blood, abdominal adipose tissue and skeletal muscle for molecular analysis and respiratory measurements at rest.
Experimental: Young obese men
BMI [30, 40] Age [18, 40]
Other: Diet
Long-term fasting (84 hours), physiological testing before and after fasting: sampling of blood, abdominal adipose tissue and skeletal muscle for molecular analysis and respiratory measurements at rest.
Experimental: Young obese women
BMI [30, 40] Age [18, 40]
Other: Diet
Long-term fasting (84 hours), physiological testing before and after fasting: sampling of blood, abdominal adipose tissue and skeletal muscle for molecular analysis and respiratory measurements at rest.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
The effect of fasting and obesity on protein glycosylation of the extracellular matrix in adipose tissue
Time Frame: The fasting will last approximately 84 hours.
The composition and protein glycosylation of the extracellular matrix will be measured in abdominal subcutaneous adipose tissue samples in 20 healthy normal weight men and women and 20 healthy obese men and women.
The fasting will last approximately 84 hours.

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
The effect of fasting and obesity on peak fat oxidation
Time Frame: The fasting will last approximately 84 hours
40 participants (20 healthy normal weight men and women and 20 healthy obese men and women) will fast for 84 hours. Before and after the fast, peak fat oxidation (mg fat/min) is measured in an incremental bike test using indirect calorimetry.
The fasting will last approximately 84 hours

Other Outcome Measures

Outcome Measure
Measure Description
Time Frame
The effect of fasting and obesity on adipose tissue lipolytic capacity, muscle ketone oxidative capacity and mitochondrial coupling.
Time Frame: The fasting will last approximately 84 hours.
The lipolytic capacity will be measured in abdominal subcutaneous adipose tissue samples and the capacity for ketone oxidation in vastus lateralis muscle in 20 healthy normal weight men and women and 20 healthy obese men and women.and In addition mitochondrial respiratory capacity will be measured in the muscle and adipose biopsy samples using high-resolution respirometry (Oxygraphs, Oroboros).
The fasting will last approximately 84 hours.

Collaborators and Investigators

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

Sponsor

University of Copenhagen

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)

June 1, 2026

Primary Completion (Estimated)

August 1, 2027

Study Completion (Estimated)

December 1, 2033

Study Registration Dates

First Submitted

June 19, 2026

First Submitted That Met QC Criteria

July 2, 2026

First Posted (Actual)

July 9, 2026

Study Record Updates

Last Update Posted (Actual)

July 9, 2026

Last Update Submitted That Met QC Criteria

July 2, 2026

Last Verified

June 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • Molecular Memory of Obesity

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

When the experiments are concluded and the paper(s) are accepted that data will be able upon reasonable request

IPD Sharing Time Frame

The data will be available after publication and indefinately

IPD Sharing Access Criteria

Not known at this state

IPD Sharing Supporting Information Type

  • STUDY_PROTOCOL
  • SAP
  • CSR

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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