How Differences in the Composition of Microorganisms in the Soil Affect the Microorganisms in the Human Gut, Through the Vegetables That Grow in it: a Process Pilot Study With Healthy Participants (HUMANITAS)

July 29, 2026 updated by: Pieter Maljaars, Leiden University Medical Center

The Effect of Soil Biodiversity on Human Gut Microbiome: a Process Pilot Study (The HUMANITAS Study)

There are two objectives for this clinical trial. The first is to test whether, with the current logistics and study setup it is possible to perform the study well and see where there might be bottlenecks we couldn't predict. The second objective is to investigate the relation between the composition of the microorganisms in the soil, the crops that grow in that soil, and the human gut. During the study participants will drink three vegetable smoothies a day, for two periods of one week. The only difference between the two periods is whether the vegetables come from a farm with a low diversity of microorganisms in the soil or a high diversity. Participants will be asked to give blood samples and turn in fecal samples before and after each period.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Not yet recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Detailed Description

This randomized, double-blind, crossover pilot study will be used to assess the feasibility of logistics including vegetable delivery and preparation of the intervention product by the participants themselves. Besides feasibility, we will aim to identify live bacteria and fungi present in the intervention product (smoothies) and trace these back in stool samples.

The gut microbiome is also called the "second genome" to which many protective and life-supporting functions have been externalized. It orchestrates the crosstalk between our own cells and environmental metagenome. Diet and food choices can modulate gut microbiome species and functional diversity, but the mechanisms by which this occurs are unclear. The nutritional quality of crops, the crop microbiome and the soil microbiome may therefore all be involved.

Ten participants will be randomized in a cross-over design, with each participant drinking three 150 mL vegetable smoothies per day for two separate intervention weeks (HiDi vs LoDi soil origin, randomized 1 : 1). During the first week, smoothies will be prepared with the vegetables derived from microbiome-enriched soil (HiDi) or microbiome-impoverished soil (LoDi). Vegetables, a blender, and detailed instructions to prepare the smoothies on-site will be delivered to the participant. Each participant is asked to keep a diary (in the form of a daily Castor questionnaire), with special attention to dietary habits and intake. Furthermore, before and after this specified diet week, blood and stool samples will be collected. After a washout period of two weeks, participants will be offered identical meals in a crossover design.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
10

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • 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

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Contact Backup

Study Locations

  • Netherlands
    • South Holland
      • Leiden, South Holland, Netherlands, 2333ZA
        • Leids Universitair Medisch Centrum
        • Contact:
        • Principal Investigator:
          • Jeroen Maljaars, MD, PhD

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

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Aged 18 to 70 years
  • Written informed consent
  • Inhabitant of Leiden

Exclusion Criteria:

  • Any documented causes of chronic disease
  • Suspicion of or present excessive alcohol use defined as >2 units/day (>14/week)
  • Recent use (<3 months) of antibiotics
  • Any known food allergy or restriction, or following a vegan/vegetarian diet
  • Use of possible drugs interfering microbiota or recent (< 3 months) changes in dosages
  • A psychiatric, addictive or any other disorder that compromises the participants ability to understand the study content and to give written informed consent for participation in the 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: Prevention
  • Allocation: Randomized
  • Interventional Model: Crossover Assignment
  • Masking: Triple

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Active Comparator: Crops derived from Low followed by High diversity soil
Participants will be given vegetables, originating from low- or high-microbial diversity soil, to prepare smoothies with. In this arm participants start with vegetables from a low diversity soil, after a washout period of two weeks they will receive vegetables from a high diversity soil.
Other: Low diversity vegetable smoothie
Vegetable smoothie prepared with crops grown in low-microbial diversity soil
Other: High diversity vegetable smoothie
Vegetable smoothie prepared with crops grown in high-microbial diversity soil
Active Comparator: Crops derived from High followed by Low diversity soil
Participants will be given vegetables, originating from low- or high-microbial diversity soil, to prepare smoothies with. In this arm participants start with vegetables from a high diversity soil, after a washout period of two weeks they will receive vegetables from a low diversity soil.
Other: Low diversity vegetable smoothie
Vegetable smoothie prepared with crops grown in low-microbial diversity soil
Other: High diversity vegetable smoothie
Vegetable smoothie prepared with crops grown in high-microbial diversity soil

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Feasibility of logistics of the study protocol: Deliveries
Time Frame: From start enrollment to the end of treatment at 4 weeks
The percentage of successful deliveries to the participants in the pre-agreed time window.
From start enrollment to the end of treatment at 4 weeks
Feasibility of logistics of the study protocol: Preparation of the intervention product
Time Frame: From the start of the treatment period until the end at 4 weeks
Using the Daily diary (Castor questionnaire), successful preparation of the intervention product is assessed.
From the start of the treatment period until the end at 4 weeks
Feasibility of logistics of the study protocol: Recruitment rate
Time Frame: From the start of recruitment until the start of the study
Number of recruited participants per month until the start of the study.
From the start of recruitment until the start of the study
Tracing back life microorganisms from the smoothie in stool samples
Time Frame: Day 1, Day 7, Day 22, and Day 28
Life bacteria present in the smoothies will be cultured and sequenced to then compare to feces samples of participants
Day 1, Day 7, Day 22, and Day 28

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Participant compliance to the study protocol
Time Frame: From start enrolment until the end of treatment at the end of 4 weeks
Compliance with the protocol will be assessed through the daily lifestyle diary (in the form of a Castor questionnaire). Which will capture the number of consumed smoothies (≥95.2%) and number of consumed smoothies at the correct time window (≥80%). As well whether the duration and time of exercise (≥80%), duration and time of nighttime sleeping period (≥80%), timing and content of main meals (≥80%) between the two periods are comparable. For each of the parameters the compliance threshold is indicated above. Based on these parameters we will get a percentage of participants that were compliant.
From start enrolment until the end of treatment at the end of 4 weeks
Shifts in gut microbiome composition
Time Frame: Baseline, Day 8, Day 21, and Day 29
Metagenomics will be performed on feces samples from participants to get an compositional view of the gut microbiome. Samples will be taken at baseline, Day 8, Day 21, and Day 29
Baseline, Day 8, Day 21, and Day 29
Sample completeness
Time Frame: From start of treatment to the end of treatment at 4 weeks
percentage of complete sampling sets
From start of treatment to the end of treatment at 4 weeks
Asses willingness of participants to create their own intervention product
Time Frame: From start treatment to end of treatment at 4 weeks
Using the Daily diary (Castor questionnaire), the participants are required to fill in their opinion on creating their own intervention product on a daily basis. This is measured on a 10 point scale, with 1 being equal to never wanting to do it again and 10 being equal to enjoying it. There is also an optional open question where participants can justify their answer.
From start treatment to end of treatment at 4 weeks
Differences in phytonutrient levels in serum
Time Frame: Baseline, Day 8, Day 21, and Day 29
After confirmation of significant changes in gut microbiome composition, phytonutrient levels will be measured in serum. Serum will be collected at Baseline, Day 8, Day 21, and Day 29
Baseline, Day 8, Day 21, and Day 29

Collaborators and Investigators

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

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Leiden University Medical Center

Collaborators

Collaborators

An organization other than the sponsor that provides support for a clinical study. This support may include activities related to funding, design, implementation, data analysis, or reporting.
Maastricht University

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)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
August 1, 2026

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
September 1, 2026

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
September 1, 2026

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
July 16, 2026

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
July 29, 2026

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
August 3, 2026

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
August 3, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
July 29, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
July 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • NL-010026

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

Metagenomic sequencing data from feces and pythonutrient levels in serum (if available)

IPD Sharing Time Frame

Beginning 1 month after publication with no end date

IPD Sharing Supporting Information Type

  • STUDY_PROTOCOL
  • ANALYTIC_CODE

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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