Effects Of Dietary Fats on Gut Microbiota Composition and Metabolic Activity in Healthy Adults

April 17, 2026 updated by: Athanasios Koutsos, University of Glasgow
This study will investigate how adding a specific type of dietary fat to daily meals for two weeks affects the gut bacteria and their activity. Participants will be randomly assigned to consume one of four types of fat: butter, coconut oil, olive oil, or sunflower oil (60 mL each day for 2 weeks). Stool and blood samples (after an overnight fast) will be collected at 3 time points during the study (Days 1, 7, and 22). These samples will be used to measure metabolites produced by gut bacteria, the types of bacteria present in the gut, blood lipids, and inflammatory markers. The study, based on previous in vitro findings, aims to understand whether different types of fats (based on their structure and level of saturation) have different effects on gut bacteria and their activity in healthy subjects.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Detailed Description

This is a pilot, parallel, randomised controlled dietary intervention trial investigating the effects of dietary fat composition on gut microbiota and metabolic activity in healthy adults. Participants will be randomised to one of four intervention groups (butter, coconut oil, extra virgin olive oil, or sunflower oil), representing commonly consumed dietary fats that differ in fatty acid structure.

This study builds on prior in vitro findings demonstrating that fatty acid chain length and degree of saturation influence microbial fermentation pathways and short-chain fatty acid (SCFA) production.

The primary objective is to determine whether structurally distinct dietary fats differentially influence gut microbial activity and composition in vivo. Secondary objectives include assessing the effects on cardiometabolic and inflammatory markers. It is hypothesised that dietary fats differing in chain length and degree of saturation will differentially modulate gut microbiota metabolism, with potential systemic effects on circulating cardiometabolic and inflammatory markers.

A total of 64 healthy adults aged 20-50 years will be recruited from the Glasgow area. All study visits will take place at the New Lister Building, University of Glasgow. Participants will attend three study visits over a three-week period.

The study includes a one-week run-in period (normal habitual diet) followed by a two-week dietary intervention. During the intervention, participants will replace the majority of their habitual dietary fat intake with their allocated fat while maintaining their usual diet and lifestyle.

Biological samples (blood and stool) will be collected at each study visit (Day 1, 7 and 22) to assess study outcomes. Anthropometric measurements will also be recorded. Dietary intake, gastrointestinal symptoms, and compliance will be monitored using food diaries, symptom questionnaires, and adherence logs.

The sample size is based on anticipated changes in faecal SCFA concentrations. Based on prior data, 14 participants per group provides 80% power (P=0.05) to detect a mean change of 30 μmol/g (SD: 28 μmol/g). Allowing for a 10% drop-out rate, 16 participants per group (64 total) will be recruited. As this is a pilot study, this calculation is intended to inform a reasonable sample size rather than to ensure definitive hypothesis testing.

Study Type

Interventional

Enrollment (Estimated)

64

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 Contact Backup

Study Locations

  • United Kingdom
      • Glasgow, United Kingdom, G31 2ER
        • Recruiting
        • New Lister Building, Glasgow Royal Infirmary, 10-16 Alexandra Parade, G31 2ER
        • Contact:
        • Principal Investigator:
          • Athanasios Koutsos

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:

  • Adults aged 20-50 years
  • Body mass index (BMI) between 20 and 30 kg/m²
  • Generally healthy
  • Stable body weight (±2 kg) over the past 2 months
  • Living in the Glasgow area
  • Non-smoker

Exclusion Criteria:

  • Use of antibiotics within the past 3 months
  • Current use of medications affecting gut microbiota or cardiometabolic health
  • Regular use of dietary supplements that may influence study outcomes (e.g. probiotics, prebiotics, vitamins, minerals, fish oil), unless willing to discontinue prior to study start
  • Presence of chronic gastrointestinal, metabolic, cardiovascular, hepatobiliary, or pancreatic disease
  • History of major gastrointestinal surgery
  • Diagnosed diabetes or use of lipid-lowering therapy
  • Known fat malabsorption disorders
  • Pregnant or lactating women
  • Post-menopausal women
  • Following a restrictive or specific diet (e.g. vegan, ketogenic diet)
  • Food allergies or intolerances relevant to study interventions (e.g. dairy, coconut)
  • Recent significant weight change (±2 kg in the past month)
  • High reliance on ready meals or takeaway foods (>7 main meals per week)
  • Participation in another research study that may interfere with this study

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: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Butter
Following a one week run-in period (habitual diet), participants will be assigned to consume butter as their primary dietary fat.
Other: Butter
Participants will consume approximately 65 g/day of butter as their primary dietary fat for 14 days, replacing most habitual dietary fat intake.
Experimental: Coconut Oil
Following a one week run-in period (habitual diet), participants will be assigned to consume coconut oil as their primary dietary fat.
Other: Coconut oil
Participants will consume approximately 55 g/day of coconut oil as their primary dietary fat for 14 days, replacing most habitual dietary fat intake.
Experimental: Extra Virgin Olive Oil
Following a one week run-in period (habitual diet), participants will be assigned to consume olive oil as their primary dietary fat.
Other: Extra Virgin Olive Oil
Participants will consume 60 mL/day of olive oil as their primary dietary fat for 14 days, replacing most habitual dietary fat intake.
Experimental: Sunflower Oil
Following a one week run-in period (habitual diet), participants will be assigned to consume sunflower oil as their primary dietary fat.
Other: Sunflower Oil
Participants will consume 60 mL/day of sunflower oil as their primary dietary fat for 14 days, replacing most habitual dietary fat intake.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Change in faecal short-chain fatty acid (SCFA) concentrations
Time Frame: Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Faecal concentrations of short-chain fatty acids (acetate, propionate, and butyrate) will be measured using gas chromatography to assess changes in gut microbial metabolic activity in response to dietary fat intervention.
Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Change in gut microbiota composition
Time Frame: Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Gut microbiota composition will be assessed using 16S rRNA gene amplicon sequencing to evaluate changes in bacterial diversity and relative abundance following the dietary fat intervention.
Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Change in blood lipid profile
Time Frame: Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Fasting blood concentrations of total cholesterol, LDL-cholesterol, HDL-cholesterol, and triglycerides will be measured using standard enzymatic assays to assess cardiometabolic responses to the dietary fat intervention.
Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Change in inflammatory markers
Time Frame: Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Circulating inflammatory markers (e.g., C-reactive protein (CRP), interleukin-6 (IL-6)) will be measured using ELISA or multiplex assays to assess systemic inflammatory responses to the dietary fat intervention.
Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Change in faecal pH
Time Frame: Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Faecal pH will be measured to assess changes in the gut environment associated with microbial fermentation.
Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Change in fasting glucose concentrations
Time Frame: Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Fasting blood glucose concentrations will be measured to assess changes in glucose metabolism in response to dietary fat intake.
Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Change in faecal fat content
Time Frame: Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)
Faecal fat content will be measured to assess fat excretion and potential differences in fat digestion and absorption across intervention groups.
Day 1 (pre run-in), Day 7 (baseline, post run-in), and Day 22 (post-intervention)

Collaborators and Investigators

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

Sponsor

University of Glasgow

Collaborators

Dr Dalia Malkova
Professor Konstantinos Gerasimidis

Investigators

  • Principal Investigator: Konstantinos Gerasimidis, PhD, University of Glasgow
  • Principal Investigator: Athanasios Koutsos, University of Glasgow
  • Principal Investigator: Dalia Malkova, PhD, University of Glasgow

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)

March 23, 2026

Primary Completion (Estimated)

March 31, 2027

Study Completion (Estimated)

March 31, 2028

Study Registration Dates

First Submitted

April 17, 2026

First Submitted That Met QC Criteria

April 17, 2026

First Posted (Actual)

April 24, 2026

Study Record Updates

Last Update Posted (Actual)

April 24, 2026

Last Update Submitted That Met QC Criteria

April 17, 2026

Last Verified

April 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 200250221

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

UNDECIDED

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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