The Role of the Mediterranean Diet in Breast Cancer Survivorship: A Systematic Review and Meta-Analysis of Observational Studies and Randomised Controlled Trials

Abstract

Female breast cancer is the most frequently diagnosed cancer. The long-term survival rates for this disease have increased; however, the unique demand for high-quality healthcare to improve breast-cancer survivorship are commonly unmet. The Mediterranean diet (MD) is associated with reduced breast-cancer risk and various health-related benefits in the general population, but its effect on breast-cancer survivors remains uncertain. The objective of this systematic review and meta-analysis was to assess current evidence from randomised controlled trials (RCTs) and observational studies (cohort, cross-sectional and case-control) regarding the effect of the MD on survival, quality of life (QoL) and health-related outcomes in female breast-cancer survivors. MEDLINE, EMBASE, Web of Science and the Cochrane library were searched for studies published before and including April 2022. Two reviewers independently screened the literature and completed the data extraction and risk-of-bias assessment. Eleven studies (fifteen reports) were included, including two RCTs, four cohort and five cross-sectional studies. The meta-analysis of the cohort studies showed strong evidence of an inverse association between high adherence to the MD and all-cause mortality (hazard ratio (HR) 0.78, 95% confidence interval (CI) 0.66–0.93, I2: 0%, Grading of Recommendations Assessment, Development and Evaluation (GRADE) = low certainty of evidence) and non-breast-cancer mortality (HR 0.67, 95% CI 0.50–0.90, I2: 0%, GRADE = very low certainty of evidence). The associations between high adherence to the MD and QoL and health-related parameters were not consistent. These findings highlight the potential of adherence to the MD to reduce the risk of mortality. Future research with better study designs, as well as more consistent measurements of QoL and MD adherence, taking into account changes in MD adherence over time and population subgroups, is needed to provide more robust evidence on the survival, QoL and health-related outcomes in BC survivors.

Effects of Functional and Nutraceutical Foods in the Context of the Mediterranean Diet in Patients Diagnosed with Breast Cancer

“…In particular, a systematic review and meta-analysis of observational studies and randomized controlled trials has shown that high adherence to the MD is associated with a reduced risk of all-cause mortality among BCS [271].…”

“…As regards BC, a high adherence to the MD is associated with benefits in terms of both prevention and improvement of clinical outcomes [271,278]. The combination of foods with nutraceutical properties and the richness in bioactive compounds of many typical foods of the MD such as fresh vegetables, fruit, and EVOO could exhibit multiple anticancer effects.…”

“…These results might be attributed to the small sample sizes of the studies included in the systematic review and meta-analysis or the different cut-off points used for assessing the adherence to the Mediterranean diet. Therefore, more studies are needed to strengthen the evidence for all these findings [271].…”

Breast cancer survivorship

“…Although no specific diet has been proven to prevent cancer recurrence, the Mediterranean diet is an anti‐inflammatory and antioxidant plant‐based diet that consists of fruits, vegetables, nuts, legumes, and olive oil. Strict adherence to this diet, which limits alcohol, sweets, and red meat, has been shown to decrease breast cancer risk and improve health parameters 54 …”