Systematic review and meta-analysis of diet quality and colorectal cancer risk: is the evidence of sufficient quality to develop recommendations?

Abstract

The quality of existing evidence about the impact of diet quality on colorectal cancer (CRC) risk has only rarely been assessed. In the current review, we searched PubMed, EMBASE, Web of Science, Cochrane, and the resulting references (up to January 2020) for studies that evaluated the role of high diet quality by extreme dietary index categorization and the risk of CRC. Two researchers independently performed the study selection, data extraction, and quality assessment. We then applied a random-effects meta-analysis to estimate the pooled odds ratios (ORs) and 95% confidence intervals (CIs) for CRC at the extremes of each dietary index, and we assessed the quality of the pooled results using the Grading of Recommendations Assessment, Development and Evaluation approach. A high diet quality was significantly associated with reduced CRC risk when patients had a low Diet Inflammatory Index score (OR, 0.66; 95%CI, 0.56–0.78), a high Mediterranean Diet Score (OR, 0.84; 95%CI, 0.78–0.90), high Dietary Approaches to Stop Hypertension adherence (OR, 0.83; 95%CI, 0.78–0.89), and a high Healthy Eating Index score (OR, 0.72; 95%CI, 0.64–0.80). The pooled results for all dietary indices were rated as being of low quality due to concerns over inconsistency or imprecision. We conclude that, despite a high diet quality appearing to have a preventive role in CRC, the evidence is currently of insufficient quality to develop dietary recommendations.

Keywords:

• Colorectal neoplasms
• healthy diet
• gastrointestinal neoplasms

Acknowledgements

We thank Karin Sijtsma (UMCG) for her assistance in formulating the search strategy.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Box 1. The dietary indices used to quantify diet quality.

Additional information

Funding

This research received no external funding. SM is supported by a PhD scholarship from the University of Groningen, Groningen, The Netherlands.

Notes on contributors

Sara Moazzen

SM designed the study, conducted the study, ran the data analyses, and prepared the first draft of the manuscript. BZA and GHdB designed the study, conceived the study, and edited the manuscript. SM and KWJS independently ran the search strategy, extracted the data, and assessed the quality of the included studies and pooled findings. GHdB and BZA commented on the study design, data analyses, inference of the results, and critically edited the manuscript. All authors read and approved the final manuscript draft.

Kimberley W. J van der Sloot

SM designed the study, conducted the study, ran the data analyses, and prepared the first draft of the manuscript. BZA and GHdB designed the study, conceived the study, and edited the manuscript. SM and KWJS independently ran the search strategy, extracted the data, and assessed the quality of the included studies and pooled findings. GHdB and BZA commented on the study design, data analyses, inference of the results, and critically edited the manuscript. All authors read and approved the final manuscript draft.

Geertruida H. de Bock

SM designed the study, conducted the study, ran the data analyses, and prepared the first draft of the manuscript. BZA and GHdB designed the study, conceived the study, and edited the manuscript. SM and KWJS independently ran the search strategy, extracted the data, and assessed the quality of the included studies and pooled findings. GHdB and BZA commented on the study design, data analyses, inference of the results, and critically edited the manuscript. All authors read and approved the final manuscript draft.

Behrooz Z. Alizadeh

SM designed the study, conducted the study, ran the data analyses, and prepared the first draft of the manuscript. BZA and GHdB designed the study, conceived the study, and edited the manuscript. SM and KWJS independently ran the search strategy, extracted the data, and assessed the quality of the included studies and pooled findings. GHdB and BZA commented on the study design, data analyses, inference of the results, and critically edited the manuscript. All authors read and approved the final manuscript draft.