Longitudinal associations of dietary intake with fatigue in colorectal cancer survivors up to 1 year post-treatment, and the potential mediating role of the kynurenine pathway

Introduction: A healthy diet may help to reduce cancer-related fatigue, but evidence is limited and mechanisms remain unclear. Both diet and fatigue following colorectal cancer (CRC) have been linked to metabolites (kynurenines) of the kynurenine pathway (KP). We investigated longitudinal associations between dietary intake and fatigue, and the potential mediating role of the KP, in CRC survivors up to 1 year post-treatment. Methods: Measurements at 6 weeks, 6 months, and 1 year post-treatment were performed in 209 stage I-III CRC survivors. Diet was assessed by 7-day food records. Plasma kynurenines were analyzed using LC-MS/MS. Fatigue, including subjective fatigue, was assessed using validated questionnaires. To analyse longitudinal associations between diet and fatigue and to explore potential mediation by the KP, we used confounder-adjusted multilevel parallel-multiple mediator models with all kynurenines included simultaneously, and simple mediator models with established KP ratios to estimate total (c: diet-fatigue), direct (c': diet-fatigue, while controlling for mediators), metabolite-specific indirect (ab: diet-metabolite-fatigue), and total indirect (ab: diet-metabolites-fatigue) effects. Results: Higher intake of total carbohydrates and mono- and disaccharides was longitudinally associated with more subjective fatigue, while higher intake of plant protein, total fat, and unsaturated fats was associated with less subjective fatigue (c). Most associations remained statistically significant after controlling for KP metabolites, except for mono- and disaccharides (c'). All kynurenines simultaneously did not mediate longitudinal associations between diet and subjective fatigue (ab). The kynurenic acid-to-quinolinic acid (KA/QA) ratio significantly mediated associations of intakes of carbohydrate, mono- and disaccharides, alcohol, magnesium, and zinc with subjective fatigue, whereas the HKr significantly mediated the association between polysaccharide intake and subjective fatigue (ab). Conclusion: Our findings suggest that carbohydrate intake is associated with greater fatigue, while protein and fat intake are associated with lower fatigue in CRC survivors up to 1 year post-treatment. While all KP metabolites simultaneously did not significantly mediate associations between diet and fatigue in our population, the KA/QA ratio and HKr were significant mediators in several diet-fatigue associations. These results should be repeated in larger observational studies.