An interventional study of Low diversity vegetable smoothie and High diversity vegetable smoothie in Pilot Study, sponsored by Leiden University Medical Center. Not yet recruiting at 1 site in Netherlands. Open to participants aged 18 Years to 70 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-08-03.
Sponsored by Leiden University Medical Center · Not applicable, Interventional, and Prevention
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.
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.
Leiden University Medical Center is the lead sponsor of 326 studies on the registry; 106 are open to participants now.
Counted across the registry records on this site, refreshed daily.
Exclusion Criteria:
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 · Other: High diversity vegetable smoothie
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 · Other: High diversity vegetable smoothie
Vegetable smoothie prepared with crops grown in low-microbial diversity soil
Vegetable smoothie prepared with crops grown in high-microbial diversity soil
Feasibility of logistics of the study protocol: Deliveries
The percentage of successful deliveries to the participants in the pre-agreed time window.
Time frame: From start enrollment to the end of treatment at 4 weeks
Feasibility of logistics of the study protocol: Preparation of the intervention product
Using the Daily diary (Castor questionnaire), successful preparation of the intervention product is assessed.
Time frame: From the start of the treatment period until the end at 4 weeks
Feasibility of logistics of the study protocol: Recruitment rate
Number of recruited participants per month until the start of the study.
Time frame: From the start of recruitment until the start of the study
Tracing back life microorganisms from the smoothie in stool samples
Life bacteria present in the smoothies will be cultured and sequenced to then compare to feces samples of participants
Time frame: Day 1, Day 7, Day 22, and Day 28
Participant compliance to the study protocol
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.
Time frame: From start enrolment until the end of treatment at the end of 4 weeks
Shifts in gut microbiome composition
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
Time frame: Baseline, Day 8, Day 21, and Day 29
Sample completeness
percentage of complete sampling sets
Time frame: From start of treatment to the end of treatment at 4 weeks
Asses willingness of participants to create their own intervention product
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.
Time frame: From start treatment to end of treatment at 4 weeks
Differences in phytonutrient levels in serum
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
Time frame: Baseline, Day 8, Day 21, and Day 29
Plan to share: Yes — Metagenomic sequencing data from feces and pythonutrient levels in serum (if available)
Supporting information: Study protocol, Analytic code
This study is not yet recruiting, as verified in Jul 2026. You cannot join it, but the record below documents what was studied.
Get an email when the registry record changes — status, dates, results — or when someone posts here.
Sign in to followQuestions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.
Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.
Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.
Leiden University Medical Center