Post-Diagnosis Adherence to the Mediterranean Diet and Cancer Recurrence and Fatigue Outcomes in Cancer Survivors, with Emphasis on Colorectal Cancer: A Systematic Review and Meta-Analysis

Background: Cancer survivors face heightened risks of recurrence and persistent cancer-related fatigue (CRF), both of which impair quality of life. The Mediterranean Diet (MD), characterized by its antioxidant and anti-inflammatory profile, has been proposed as a potentially beneficial dietary pattern. This systematic review and meta-analysis evaluated the association between post-diagnosis MD adherence and outcomes of cancer recurrence and CRF among adult survivors, with particular attention to colorectal cancer. Methods: Systematic searches of PubMed, CINAHL, and the Cochrane Library (January 1995–May 2024) identified prospective cohort studies and randomized controlled trials (RCTs) reporting post-diagnosis MD adherence. Primary outcomes were cancer recurrence and CRF. Random-effects models were applied for recurrence analyses due to anticipated heterogeneity, while a fixed-effects model was used for CRF given the limited number of trials. Heterogeneity was assessed using the I² statistic. Risk of bias was evaluated using the Cochrane RoB 2 tool (RCTs) and ROBINS-I (cohort studies). This review was registered in PROSPERO (CRD420251248086). Results: Eight studies met inclusion criteria: six prospective cohort studies assessed recurrence (n = 6697), and two RCTs assessed CRF (n = 76). For recurrence, higher post-diagnosis MD adherence was associated with a lower hazard of recurrence or cancer-specific mortality (HR = 0.83; 95% CI: 0.70–0.99; I² = 49%). For CRF, the pooled effect from two independent RCTs showed no statistically significant overall effect (MD = 0.29; 95% CI: −0.58 to 1.16). Both outcomes were limited by small study numbers and methodological heterogeneity. Conclusions: Higher adherence to the Mediterranean Diet after cancer diagnosis was associated with recurrence-related outcomes in observational studies, while evidence for CRF remains exploratory and statistically imprecise. Larger, adequately powered randomized trials are needed to clarify the role of the Mediterranean Diet in survivorship care.