The impact of dietary patterns and the main food groups on mortality and recurrence in cancer survivors: a systematic review of current epidemiological literature

Objective: To determine whether there is an association between dietary patterns/indices and foods from the main food groups (highest versus lowest intakes) prior to or after cancer diagnosis and mortality and cancer recurrence in cancer survivors.

Participants: Survivors of common cancers with a 10-year survival rate of 50% or more: bladder, bowel, breast, cervical, kidney, laryngeal, prostate, testicular, uterine cancer, malignant melanoma, and (non-)Hodgkin lymphoma.

Outcome measures: Mortality (overall, cancer-specific, from other causes) and cancer recurrence.

Information sources: PubMed, Embase and the Cochrane Library were searched from inception to April 2017. Additional studies were identified by searching reference lists. Two authors independently screened titles and abstracts, assessed study quality, and extracted the data.

Results: A total of 38 studies were included. The risk of bias was rated low for the included RCTs and moderate for the cohort studies. The quality of evidence was assessed with the GRADE approach and was rated moderate (RCTs), and (very)low (cohort studies). Reducing the amount of fat after diagnosis appears to decrease the risk of breast cancer recurrence. Adherence to a high-quality diet and prudent diet after diagnosis appears to decrease the risk of death from other causes (and overall mortality for high-quality diet) in breast cancer survivors. Adherence to a Western diet, before and after diagnosis, appears to increase the risk of overall mortality and death from other causes amongst breast cancer survivors. Evidence from studies amongst other cancer survivors were too limited or could not be identified.
Conclusion: For many cancer survivors, there is little evidence to date to indicate that particular dietary behaviours influence outcomes with regard to recurrence and mortality. Notwithstanding, limited evidence suggests that a low-fat diet, a high-quality diet, and a prudent diet are beneficial for breast cancer survivors, whilst a Western diet is detrimental for breast cancer survivors.

Strengths and limitations

- Dietary patterns/indices and whole foods reflect the complexity of dietary intake and capture synergistic relationships between various dietary constituents
- Most studies investigating dietary patterns/indices and foods before diagnosis do not consider potential modifications in dietary intake after cancer diagnosis
- Cohort studies provide weaker empirical evidence than RCTs for examining relationships between dietary exposure and mortality and cancer recurrence