Modified Mediterranean Diet Trial Targets Chemotherapy Side Effects Through Microbiome Modulation

Can a Modified Mediterranean Diet Improve Chemotherapy Tolerability?

Vimercate Hospital researchers have launched a pioneering clinical trial investigating whether a Modified Mediterranean Diet (MMD) can reduce chemotherapy side effects in metastatic colorectal cancer patients by favorably altering gut microbiota composition. The pilot study (NCT06794931) randomizes patients to either the MMD or a Standard Western Diet (SWD) to assess differences in microbial diversity and gastrointestinal toxicity during first-line chemotherapy treatment.

The trial, which received ethics approval from the Ethics Committee Lombardia 2 in Milan (reference R1926/24 – L2-130), represents one of the first precision nutrition interventions in oncology. By October 2024, recruitment had begun with 17 participants already enrolled. The study is designed as a prospective, randomized, controlled, single-center trial with a 1:1 allocation ratio between the MMD and SWD arms. Researchers will collect fecal samples at baseline and after the third and sixth chemotherapy cycles to analyze changes in the gut microbiome, particularly focusing on the Firmicutes:Bacteroidetes ratio as the primary endpoint. The study team hypothesizes that the MMD, rich in prebiotic fibers, resistant starches, and polyphenols, will promote beneficial bacterial growth and reduce inflammation, potentially mitigating chemotherapy-induced gastrointestinal toxicity. Secondary endpoints include the percentage of patients experiencing gastrointestinal side effects and changes in overall microbiome composition through alpha-diversity (Shannon index) and beta-diversity (Weighted Unifrac) measurements. The trial aims to enroll 40 patients (20 per arm) to account for potential dropouts, with results expected by January 2028. Participants in the MMD arm will follow a personalized dietary plan that emphasizes foods containing high-quality prebiotic fibers while limiting total fiber content to reduce gastrointestinal side effects associated with chemotherapy. The diet incorporates resistant starches to promote beneficial bacteria like Faecalibacterium prausnitzii, polyphenol-rich foods such as brown rice and extra virgin olive oil, fermented products with low lactose content, and omega-3-rich fish varieties.

What Impact Does the Gut Microbiome Have on Cancer Treatment?

The study builds on mounting evidence that gut microbiota significantly influences cancer treatment efficacy and toxicity. Recent research has demonstrated that specific bacterial compositions can enhance responses to immunotherapy in melanoma patients. Dr. Luca Gervasi, principal investigator, noted, "This will be the first evaluation of the impact of diet on chemotherapy side effects in colorectal cancer patients in a precision nutrition trial. We expect that improvements in therapy tolerability may also have implications for treatment efficacy by reducing dose delays, nutritional decay following gastrointestinal events, and therapy discontinuation." The researchers anticipate that the MMD will promote the growth of beneficial bacteria that produce short-chain fatty acids (SCFAs), particularly butyrate, which maintains intestinal barrier integrity and reduces inflammation. The trial's metabolomic analysis will identify distinct SCFA profiles and other microbial-derived metabolites that differentiate the two dietary arms, potentially revealing which dietary pattern best supports anti-tumor immunity while reducing treatment-related toxicity. Metagenomic sequencing will be performed on fecal samples to characterize the gut microbiota composition, with bioinformatics analysis using established pipelines including QIIME and the SILVA 16S rRNA database.

The trial's design aligns with recent findings from the "DIET Study" presented at ASCO 2025, which demonstrated that melanoma patients randomized to a high-fiber diet experienced significantly improved objective response rates and a marked reduction in immune-related adverse events compared to those on a low-fiber diet. Similarly, a recent exploratory study of breast cancer patients treated with CDK4/6 inhibitors found specific fecal microbiota profiles associated with treatment response, with Bifidobacterium longum and Ruminococcus callidus enriched in responders. The MIC-1 study team has emphasized the importance of patient compliance with the dietary intervention, providing flexible substitution options for foods patients find unpalatable while maintaining the therapeutic rationale. "Our exploration of possibly impacting clinical outcomes by improving chemotherapy tolerability with an appropriate diet may generate hypotheses for future properly powered studies," explained Dr. Gervasi. The team plans to disseminate findings through international publications, conference presentations, and collaboration with patient advocacy groups to ensure information reaches both medical professionals and patients.

What Does the Future Hold for Integrating Nutrition in Oncology?

Beyond the immediate clinical implications, the MIC-1 trial represents a growing trend in oncology toward integrating nutritional approaches with conventional treatments. As pharmaceutical companies increasingly explore the therapeutic potential of microbiome modulation, dietary interventions offer a complementary, non-pharmacological strategy to enhance treatment efficacy and reduce toxicity. The study's focus on both clinical outcomes and mechanistic insights through metabolomic analysis positions it at the intersection of precision medicine and nutritional science, potentially informing future development of targeted dietary recommendations for cancer patients based on individual microbiome profiles.

How Is the Industry Responding to Nutritional Innovations in Cancer Care?

Industry Context: This trial reflects the growing recognition of diet and microbiome as critical factors in cancer treatment outcomes, challenging the traditional pharmaceutical-centric approach to supportive care. As major oncology players increasingly invest in microbiome research and precision nutrition, studies like MIC-1 provide valuable insights for developing complementary strategies to conventional treatments. The integration of metabolomic and metagenomic analyses also highlights the shift toward multi-omics approaches in clinical research, enabling more precise characterization of how dietary interventions affect biological pathways relevant to treatment response and toxicity.

Summary

Researchers at Vimercate Hospital have initiated a groundbreaking clinical trial examining whether a Modified Mediterranean Diet can reduce chemotherapy-related side effects in patients with metastatic colorectal cancer by positively influencing gut microbiota composition. The prospective, randomized study (NCT06794931) compares the Modified Mediterranean Diet against a Standard Western Diet in 40 patients undergoing first-line chemotherapy, analyzing changes in gut microbiome diversity and gastrointestinal toxicity. The Modified Mediterranean Diet emphasizes prebiotic fibers, resistant starches, polyphenols, and omega-3-rich foods designed to promote beneficial bacterial growth and reduce inflammation. Primary endpoints include the Firmicutes:Bacteroidetes ratio, while secondary measures encompass gastrointestinal side effects and overall microbiome composition changes. The trial builds on emerging evidence linking gut microbiota to cancer treatment efficacy and toxicity, with recent studies demonstrating that specific bacterial compositions enhance immunotherapy responses and that high-fiber diets improve treatment outcomes in melanoma patients. Principal investigator Dr. Luca Gervasi anticipates that improved therapy tolerability may reduce dose delays, nutritional decline, and treatment discontinuation, potentially enhancing overall treatment efficacy. The study incorporates metabolomic analysis to identify distinct short-chain fatty acid profiles and microbial-derived metabolites that differentiate dietary patterns, aiming to reveal which approach best supports anti-tumor immunity while minimizing treatment-related toxicity. With results expected by January 2028, this precision nutrition intervention represents a paradigm shift in oncology supportive care, moving toward integrating nutritional approaches with conventional treatments and potentially informing future personalized dietary recommendations based on individual microbiome profiles.