The Effects of 24-hour Fasting or Carbohydrate Restriction on Postprandial Metabolic Responses

November 18, 2025 updated by: Guoda Karoblyte, University of Bath

The Acute Effects of Energy and Carbohydrate Restriction on Postprandial Metabolism

Most individuals spend the majority of the day in a fed state, making postprandial blood glucose and lipid regulation a central component of metabolic health. Short periods of fasting or reduced carbohydrate intake can occur frequently in daily life, whether through intentional dietary practices (e.g. intermittent fasting), cultural or religious traditions, or unstructured eating patterns. These periods can induce measurable metabolic changes, but the acute effects of a single 24-hour period of fasting or carbohydrate restriction on postprandial metabolism upon refeeding remain poorly characterised.

This study will examine how 24 hours of either complete fasting or low carbohydrate intake without energy restriction influence postprandial blood glucose and lipid concentrations, as well as related metabolic markers, in healthy adults, in comparison to a habitual high carbohydrate control diet. Participants will complete all three conditions in a randomised order, consuming a standardised meal test after each 24-hour condition. Repeated blood sampling and gas exchange measurements will be carried out to assess postprandial metabolic responses.

The aim of this study is to characterise whether acute periods of fasting and low carbohydrate restriction elicit distinct or comparable alterations in postprandial metabolic responses. A clearer understanding of these acute physiological effects can help inform how variations in eating patterns influence glucose and lipid handling in individuals without metabolic disease.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Study Type

Interventional

Enrollment (Actual)

16

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 Locations

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:

  • Aged between 18-40 years
  • Have a BMI of 18.5-29.9 kg/m2

Exclusion Criteria:

  1. Diagnosed with any major chronic conditions (e.g. type 2 diabetes, coronary heart disease, cancer, chronic kidney disease, etc.)
  2. Use of medication that may interfere with study outcomes (e.g. glucose or lipid-lowering medications)
  3. Currently or recently pregnant (within last 6 months), planning to get pregnant or currently lactating
  4. Has a habitually low carbohydrate intake (<150g carbohydrates/day)
  5. Current or previous eating disorder
  6. Has donated more than 500ml of blood in the last 3 months prior to the initial laboratory visit
  7. Insufficient mental capacity or language skills to independently understand and follow the study protocol
  8. Has an irregular sleeping pattern (e.g. due to undertaking night-shift work)
  9. Any other condition, concurrent intervention or behaviour deemed either to pose undue personal risk to the participant or to introduce bias into the experiment

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: Randomized
  • Interventional Model: Crossover Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
No Intervention: Habital control diet
100% of energy requirements, ≥150 carbohydrate/day
Experimental: Fasting
No energy intake
Behavioral: Fasting
No food intake for 24 hours
Experimental: Carbohydrate Restriction
100% of energy requirements, ≤20g carbohydrate
Behavioral: Carbohydrate restriction
Restriction of dietary carbohydrate to ≤5% of total energy intake for 24 hours
Other Names:
  • Ketogenic diet

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Triglyceride Concentration
Time Frame: After each 24-hour dietary condition
Plasma triglyceride concentrations assessed at baseline and postprandially for 2 hours after a mixed meal test
After each 24-hour dietary condition
Glucose Concentration
Time Frame: After each 24-hour dietary condition
Plasma glucose concentrations assessed at baseline and postprandially for 2 hours after a mixed meal test
After each 24-hour dietary condition

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Insulin Concentration
Time Frame: After each 24-hour dietary condition
Plasma insulin concentrations assessed postprandially for 2 hours after a mixed meal test
After each 24-hour dietary condition
Non-esterified Fatty Acid Concentration
Time Frame: After each 24-hour dietary condition
Plasma non-esterified fatty acid concentrations assessed at baseline and postprandially for 2 hours after a mixed meal test
After each 24-hour dietary condition
Beta-hydroxybutyrate Concentration
Time Frame: After each 24-hour dietary condition
Plasma beta-hydroxybutyrate concentrations assessed at baseline and postprandially for 2 hours after a mixed meal test
After each 24-hour dietary condition
Substrate Oxidation
Time Frame: After each 24-hour dietary condition
Lipid and carbohydrate oxidation assessed via indirect calorimetry at baseline and during 2-hour mixed meal test
After each 24-hour dietary condition

Collaborators and Investigators

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

Sponsor

University of Bath

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)

October 16, 2023

Primary Completion (Actual)

January 20, 2024

Study Completion (Actual)

November 6, 2025

Study Registration Dates

First Submitted

November 18, 2025

First Submitted That Met QC Criteria

November 18, 2025

First Posted (Actual)

November 26, 2025

Study Record Updates

Last Update Posted (Actual)

November 26, 2025

Last Update Submitted That Met QC Criteria

November 18, 2025

Last Verified

November 1, 2025

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 0590

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

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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