An interventional study of Modified Plant-Based Mediterranean Diet in Colorectal Polyp, Inflammation and Dietary Intervention, sponsored by University of California, San Diego. Enrolling by invitation at 1 site in United States. Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-05-05.
Sponsored by University of California, San Diego · Not applicable, Interventional, and Diagnostic
This study aims to investigate the impact of various healthy diets, specifically a modified plant-based Mediterranean diet, on the gut microbiome and overall well-being post-colonoscopy. The investigators hypothesize that certain diets can positively influence gut bacteria, reducing inflammation and enhancing metabolic signals.
To explore this, they will utilize metagenomic testing on stool samples to analyze the DNA of gut microorganisms. Additionally, they will conduct immune profiling on serum samples and perform metabolomic analysis to comprehensively evaluate the diet-induced changes in immune response and metabolic pathways. This multi-faceted approach will help them understand how dietary changes affect the composition and function of the gut microbiome, immune function, and overall metabolism.
An altered intestinal gut microbiota, i.e. dysbiosis, has been associated with the development of intestinal diseases including inflammatory bowel disease, colorectal cancer (CRC), and metabolic diseases such as obesity, type 2 diabetes mellitus (T2DM), and cardiovascular disease. Metagenomic analyses have revealed microbial biomarkers and ecological signatures in the fecal microbiome of CRC patients, correlating with chronic inflammation and gut dysbiosis. These factors have demonstrated prognostic relevance for CRC akin to other precursors, including conventional adenoma and serrated polyps.
Bowel lavage, a standard practice for facilitating colonoscopies, may affect the interaction between gut microbes and intestinal phenotypes. Standard bowel preparations have immediate impacts on gut microbiota composition, with alterations typically lasting around 14 days before a partial return to baseline. These changes in gut microbial diversity likely contribute to minor colonoscopy complications such as abdominal discomfort, bloating, diarrhea, and constipation during the recovery period.
Post-bowel lavage dietary intervention could potentially minimize lavage-associated side effects by promoting microbial diversity restoration and systemic inflammation reduction. In a previous mouse study, the investigators discovered that the Standard American Diet (SAD) led to the proliferation of opportunistic pathogens following surgical lavage. This change in microbial composition was linked to increased systemic inflammation and a higher incidence of surgical complications. Additionally, they observed that a high-fiber, low-saturated-fat diet-like a whole food, plant-based (WFPB), Med/DASH diet, and modified Mediterranean diet-can reverse this inflammatory phenotype.
However, there is a lack of interventional trials investigating the health benefits of specific dietary interventions following bowel lavage. Therefore, the investigators propose a human intervention study to assess if daily consumption of a high-fiber diet after colonoscopy will alter the intestinal microbiota, decrease inflammation, and improve digestive health.
This will be a controlled intervention study involving 30 subjects who will be enrolled on a rolling basis as they are identified during the recruitment period. The study begins with an initial visit at Week 1, where blood is collected for immune profiling and metabolomics, and participants start weekly stool collection using the S-Wipe method. At Week 2, a GutLab device is installed in participants' homes for daily stool collection. The colonoscopy occurs at Week 4, followed by a 2-week high-fiber diet provided by Thistle. Throughout the study, blood draws (6 mL) are performed at Weeks 1, 4, 6, and 8, while stool samples are collected weekly via S-Wipe and daily via GutLab. Participants log their food intake with a dietitian three times per week during Weeks 3, 5, and 7, and body composition measurements are taken before the colonoscopy and at the final visit. The study aims to quantify how dietary intervention affects post-lavage microbiome, metabolome, and immune response through analysis of blood and stool samples. Optional follow-ups at 1, 3, and 5 years will assess polyp recurrence. This design enables a comprehensive assessment of a high-fiber diet's impact on intestinal microbiota, inflammation, and digestive health in individuals with a history of polyps undergoing colonoscopy.
6,541 studies on the registry are indexed under Colorectal Neoplasms; 1,667 are open to participants now.
This study's planned enrollment of 30 is below the median of 76 across 4,800 interventional studies indexed under Colorectal Neoplasms.
Browse Colorectal Neoplasms studies →University of California, San Diego is the lead sponsor of 980 studies on the registry; 195 are open to participants now.
Of its 113 completed or terminated interventional studies of FDA-regulated products, 71 (63%) have results posted.
Compared within Colorectal Neoplasms, this study's primary condition as ClinicalTrials.gg classifies it; the registry's first condition term is Inflammation. The counts are of registry records indexed under each term, refreshed daily. How we classify →
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
1. Due for 2nd or 3rd colonoscopy with prior diagnosis of tubular, villous, or serrated polyps but no current diagnosis of CRC.
Exclusion Criteria:
Possible ethanol (alcohol) use disorder defined by Alcohol Use Disorders Identification Test (AUDIT) score of >15
Uncontrolled disease states:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
A blood test of average blood sugar over the past two to three months, given as a percentage or in mmol/mol. 6.5% (48 mmol/mol) or more is the usual threshold for diabetes, normally confirmed by a second test.
The protein in red blood cells that carries oxygen. A low level is anaemia, which can cause tiredness and breathlessness. Measured in g/dL or g/L (9 g/dL is 90 g/L).
A “mini-stroke”: temporary stroke-like symptoms caused by reduced blood flow to part of the brain, spinal cord or eye, without signs of a new stroke on a scan.
Stroke symptoms need emergency care at once, even if they go away.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HbA1c
A blood test of average blood sugar over the past two to three months, given as a percentage or in mmol/mol. 6.5% (48 mmol/mol) or more is the usual threshold for diabetes, normally confirmed by a second test.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hemoglobin (Hb)
The protein in red blood cells that carries oxygen. A low level is anaemia, which can cause tiredness and breathlessness. Measured in g/dL or g/L (9 g/dL is 90 g/L).
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
TIA (transient ischaemic attack)
A “mini-stroke”: temporary stroke-like symptoms caused by reduced blood flow to part of the brain, spinal cord or eye, without signs of a new stroke on a scan.
Stroke symptoms need emergency care at once, even if they go away.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants in this arm will follow a modified plant-based Mediterranean diet following their colonoscopies. The dietary intervention aims to reduce inflammation and improve gut microbiome composition. Participants' gut bacteria and overall health will be monitored through blood and stool sample collections, focusing on inflammation reduction and metabolic health improvement.
Dietary Supplement: Modified Plant-Based Mediterranean Diet
Two-week dietary intervention after the participants' scheduled colonoscopy consisting of vegetarian high-fiber meals. These meals are designed to provide a substantial intake of dietary fiber through a variety of plant-based foods, including whole grains, legumes, fruits, vegetables, nuts, and seeds. Meals will be delivered bi-weekly, and compliance will be monitored through regular check-ins with a study dietitian.
Changes in Inflammatory Markers and Microbial Metabolites
Measure changes in circulating inflammatory markers (e.g., CRP, IL-6, IL-8, IL-10) and microbial metabolites (e.g., short-chain fatty acids such as butyrate, propionate, and acetate) at four time-points (Weeks 1, 4, 6, and 8) following bowel lavage and adherence to a modified plant-based Mediterranean diet. Gastrointestinal discomfort will be tracked using patient-reported outcome tools, with comparisons to baseline and across all time points.
Time frame: 4 time-points throughout the study: Weeks 1, 4, 6, and 8
Changes in Gut Microbiome Composition and Opportunistic Pathogen Abundance
Measure changes in the gut microbiome composition, including alpha diversity (e.g., Shannon index, Simpson index) and beta diversity (e.g., Bray-Curtis dissimilarity, UniFrac distances), along with the abundance of opportunistic pathogens (e.g., Enterococcus faecalis). Associations will be drawn between microbial diversity and composition, colonoscopy outcomes, circulating immune/metabolite markers, and reported gastrointestinal discomfort. Daily fecal samples will undergo metagenomic sequencing and bioinformatic analysis to quantify these metrics over 7 weeks.
Time frame: 7 Weeks of fecal sampling: Weeks 2-8
Plan to share: Yes
Supporting information: Study protocol, Statistical analysis plan, Informed consent form, Clinical study report, Analytic code
No publications or documents are linked to this record.
Started Mar 2025 (actual). Primary completion is estimated for Nov 2026, 20 months after the start.
Of 898 non-industry interventional studies with no phase under Colorectal Neoplasms, half reached primary completion within 32 months of starting (the median), counting those still running; a quarter within 15 and three quarters within 62. This study's planned 20 months is below that.
Counting every sponsor, half of 955 studies reached it within 32 months; a quarter within 14 and three quarters within 60.
How these figures are worked out, and which studies are left out of them.
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