In the present study, we aimed to describe dietary changes made post-diagnosis and current dietary supplement use by survivors of colorectal cancer (CRC), and explore the underlying motives for these lifestyle habits. Cross-sectional analyses were performed for 1458 stage I–IV CRC survivors of the Patient Reported Outcomes Following Initial Treatment and Long-Term Evaluation of Survivorship (PROFILES) registry, diagnosed between 2000 and 2009. Lifestyle, sociodemographic and clinical information was collected. Prevalence of and motivations for dietary changes and supplement use were assessed. Associations between lifestyle, sociodemographic and clinical variables were analysed by multivariable logistic regression. CRC survivors (57 % male) were on average 70 (sd 9) years of age and diagnosed 7 (sd 3) years ago. Dietary changes post-diagnosis were reported by 36 % of the survivors and current supplement use by 32 %. Motivations for dietary changes were mostly cancer-related (44 % reported ‘prevention of cancer recurrence’ as the main reason), while motivations for supplement use were less frequently related to the cancer experience (38 % reported ‘to improve health and prevent disease in general’ as the main reason). Dietary changes were significantly associated with dietary supplement use (OR 1·5, 95 % CI 1·1, 2·1). Survivors who had received dietary advice, were non-smokers, under 65 years of age, and had no stoma were more likely to have changed their diet. Survivors who were female, had multiple co-morbidities, and no overweight or obesity were more likely to use supplements. In conclusion, many CRC survivors alter their diet post-diagnosis and use dietary supplements, in part for different reasons. Insights into motivations behind these lifestyle habits and characteristics of CRC survivors adopting these habits can improve the tailoring of lifestyle counselling strategies.