Efficacy of a plant-based diet on FOLFOX chemotherapy-induced gastrointestinal toxicity in patients with colorectal cancer: study protocol for a multicentre, stratified, randomised controlled trial

BACKGROUND: Gastrointestinal toxicity during FOLFOX chemotherapy for colorectal cancer (CRC) is frequent and can impair oral intake, quality of life, and planned chemotherapy delivery. Safe and scalable dietary strategies are needed as adjuncts to standard supportive care. This trial will evaluate whether a structured plant-based dietary strategy reduces chemotherapy-induced gastrointestinal toxicity (CIGT) and improves related biological and patient-centered outcomes. METHODS: This multicentre, stratified, three-arm, parallel-group, assessor-blinded, superiority randomised controlled trial will enrol 114 adults (18-65 years) with pathologically confirmed CRC receiving (or scheduled to receive) FOLFOX chemotherapy at two hospitals in Chengdu, China. Participants will be randomised (1:1:1), stratified by study site and sex, to (1) a structured plant-based dietary strategy, (2) conventional dietary guidance, or (3) conventional dietary guidance plus an oncology complete nutritional formula, for 6 weeks. Assessments will be performed at baseline and at prespecified time points through week 6. Primary outcomes are (i) the participant-level incidence of any prespecified CTCAE gastrointestinal toxicity of grade ≥ 2 during follow-up, (ii) serum inflammatory biomarkers, and (iii) stool-based profiling. Secondary outcomes include dietary intake and diet quality, body composition by bioelectrical impedance analysis, routine clinical laboratory indices, fatigue, anxiety/depression, physical activity, and adverse events. Primary analyses will follow the intention-to-treat principle. DISCUSSION: This trial will provide evidence on the efficacy and safety of a plant-based dietary strategy to mitigate CIGT during FOLFOX chemotherapy. Integrated clinical, biomarker, and stool multi-omics measures may also support exploration of biological correlates of symptom burden and treatment tolerance. TRIAL REGISTRATION: Chinese Clinical Trial Registry (ChiCTR), ChiCTR2500095215; registered 03 January 2025. https://www.chictr.org.cn/showproj.html?proj=254099 .