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Introduction A healthy lifestyle, along with regular colorectal cancer (CRC) screening, is key to reducing the risk of colorectal neoplasia (ie, precancerous lesions and CRC). However, there is limited evidence on the effect of a combined lifestyle intervention on health outcomes. This review aimed to summarise the effect of combined lifestyle interventions on behavioural change, colorectal neoplasia risk, mortality and quality of life (QoL) in people at above-average risk of CRC due to a family history of CRC or a personal history of colorectal neoplasia.Methods and analysis This systematic review and meta-analysis will be conducted according to the Cochrane guidelines. Relevant trial studies, including randomised controlled trials and non-randomised trials, will be searched across four databases: Medline/Ovid, Cochrane Library, Web of Science and Scopus. Studies that assessed the effect of at least two lifestyle interventions in people at above-average risk of CRC will be included. The primary outcome will be colorectal neoplasia risk, while behavioural change, mortality and QoL will be considered as secondary outcomes. Two independent reviewers will screen the articles, extract the data and assess the quality of included studies. The results of homogeneous studies will be synthesised through meta-analysis using a fixed-effects or random-effects model. Meta-analysis results will be reported using either relative risks or HR with 95% CIs for dichotomous outcomes and mean differences with 95% CI for continuous outcomes. Statistical heterogeneity between the studies will be evaluated using the I 2 test.PROSPERO registration number CRD420251046134.