Unhealthy dietary habits can contribute to the development of colorectal cancer (CRC). Such habits may also be associated with post-treatment symptoms experienced by CRC survivors. Therefore, we aimed to assess longitudinal associations of post-treatment unhealthy dietary habits, i.e. intake of ultra-processed foods (UPF), red and processed meat, alcohol and sugar-sweetened drinks, with health-related quality of life (HRQoL), fatigue and chemotherapy-induced peripheral neuropathy (CIPN) in CRC survivors from 6 weeks up to 24 months post-treatment. In a prospective cohort among stage I-III CRC survivors (n 396), five repeated home visits from diagnosis up to 24 months post-treatment were executed. Dietary intake was measured by 7-d dietary records to quantify consumption of UPF, red and processed meat, alcohol and sugar-sweetened drinks. HRQoL, fatigue and CIPN were measured by validated questionnaires. We applied confounder-adjusted linear mixed models to analyse longitudinal associations from 6 weeks until 24 months post-treatment. We applied a post hoc time-lag analysis for alcohol to explore the directionality. Results showed that higher post-treatment intake of UPF and sugar-sweetened drinks was longitudinally associated with worsened HRQoL and more fatigue, while higher intake of UPF and processed meat was associated with increased CIPN symptoms. In contrast, post-treatment increases in alcohol intake were longitudinally associated with better HRQoL and less fatigue; however, time-lag analysis attenuated these associations. In conclusion, unhealthy dietary habits are longitudinally associated with lower HRQoL and more symptoms, except for alcohol. Results from time-lag analysis suggest no biological effect of alcohol; hence, the longitudinal association for alcohol should be interpreted with caution.

The World Cancer Research Fund and American Institute for Cancer Research (WCRF/AICR) advise cancer survivors to follow their lifestyle recommendations for cancer prevention. Adhering to these recommendations may have beneficial effects on patient-reported outcomes after a cancer diagnosis, but evidence is scarce. We aimed to assess associations of the individual dietary WCRF/AICR recommendations regarding fruit and vegetables, fibre, fast foods, red and processed meat, sugar-sweetened drinks and alcohol consumption with patient-reported outcomes in colorectal cancer (CRC) survivors. Cross-sectional data of 150 stage I–III CRC survivors, 2–10 years post-diagnosis, were used. Dietary intake was measured by 7-d dietary records. Validated questionnaires were used to measure health-related quality of life (HRQoL), fatigue and neuropathy. Confounder-adjusted linear regression models were used to analyse associations of each WCRF/AICR dietary recommendation with patient-reported outcomes. Higher vegetable intake (per 50 g) was associated with better global QoL (β 2·6; 95 % CI 0·6, 4·7), better physical functioning (3·3; 1·2, 5·5) and lower levels of fatigue (−4·5; −7·6, −1·4). Higher fruit and vegetables intake (per 100 g) was associated with better physical functioning (3·2; 0·8, 5·5) and higher intake of energy-dense food (per 100 kJ/100 g) with worse physical functioning (−4·2; −7·1, −1·2). No associations of dietary recommendations with neuropathy were found. These findings suggest that adhering to specific dietary WCRF/AICR recommendations is associated with better HRQoL and less fatigue in CRC survivors. Although the recommendations regarding healthy dietary habits may be beneficial for the well-being of CRC survivors, longitudinal research is warranted to gain insight into the direction of associations.

The lifestyle recommendations of the World Cancer Research Fund (WCRF)/American Institute for Cancer Research (AICR) are primarily intended for cancer prevention. In the absence of specific recommendations for cancer survivors, we investigated adherence of colorectal cancer (CRC) survivors to the WCRF/AICR lifestyle recommendations and associations with health-related quality of life (HRQoL). The cross-sectional part of the Energy for life after ColoRectal cancer (EnCoRe) study was conducted in 155 CRC survivors (stage I-III), 2–10 years post diagnosis. Dietary intake, physical activity and general body fatness were measured by 7-d food diaries, by questionnaires and accelerometers and BMI, respectively. Adherence to each of the ten WCRF/AICR recommendations was scored as 0 (no/low adherence), 0·5 (moderate adherence) or 1 point (complete adherence), and summed into an overall adherence score (range: 0–10). HRQoL, disability and distress were assessed by validated questionnaires. Associations of the overall WCRF/AICR adherence score with HRQoL outcomes were analysed by confounder-adjusted linear regression. The mean adherence score was 5·1 (sd 1·4, range: 1·5–8·5). In confounder-adjusted models, a higher adherence score was significantly associated with the HRQoL dimension better physical functioning (β per 1 point difference in score: 2·6; 95 % CI 0·2, 5·1) and with less fatigue (β: −3·3; 95 % CI −6·4, −0·1). In conclusion, higher adherence of CRC survivors to WCRF/AICR lifestyle recommendations for cancer prevention was associated with better physical functioning and with less fatigue. This study adds to the limited knowledge on adherence to lifestyle behaviours in CRC survivors and relationships with quality of life. Prospective studies are needed to investigate longitudinal associations.