Red and processed meat intakes and cardiovascular disease and type 2 diabetes mellitus: An umbrella systematic review and assessment of causal relations using Bradford Hill’s criteria

Abstract

Observational research suggests higher red and processed meat intakes predict greater risks of developing or dying from cardiovascular diseases (CVD) and type 2 diabetes mellitus (T2DM), but this research limits causal inference. This systematic review of reviews utilizes both observational and experimental research findings to infer causality of these relations. Reviews from four databases were screened by two researchers. Reviews included unprocessed red meat (URM), processed meat (PM), or mixed URM + PM intake, and reported CVD or T2DM outcomes. Twenty-nine reviews were included, and causality was inferred using Bradford Hill’s Criteria. Observational assessments of CVD outcomes and all meat types consistently reported weak associations while, T2DM outcomes and PM and Mixed URM + PM assessments consistently reported strong associations. Experimental assessments of Mixed URM + PM on CVD and T2DM risk factors were predominately not significant which lacked coherence with observational findings. For all meat types and outcomes, temporality and plausible mechanisms were established, but specificity and analogous relationships do not support causality. Evidence was insufficient for URM and T2DM. More experimental research is needed to strengthen these inferences. These results suggest that red and processed meat intakes are not likely causally related to CVD but there is potential for a causal relationship with T2DM.

Keywords:

• Causation
• human adults
• nutrition
• morbidity
• mortality
• randomized controlled trial
• relative risk

Acknowledgments

We thank Andrew W Brown, PhD for his thoughtful feedback on the manuscript draft. Hill and Drs O’Connor and Campbell designed the research. McGowan, Hill, Wang, and Clark conducted the systematic review; Hill, Wang, and Dr. O’Connor conducted the research, analyzed the data, and drafted the manuscript. Hill and Dr. Campbell had full access to all the data in the review and take primary responsibility for final content. Hill, Wang, and Drs O’Connor, Campbell and Forman made critical revisions and provided intellectual content. All authors read and approved the final manuscript. This work was supported by The Beef Checkoff.

Disclosure statement

During the time this research was conducted, WWC received funding for research grants, travel or honoraria for scientific presentations, or consulting services from the following organizations: The Beef Checkoff, Pork Checkoff, North Dakota Beef Commission, Barilla Group, Mushroom Council, National Chicken Council, Foundation for Meat and Poultry Research and Education, and American Egg Board’s Egg Nutrition Center. ERH, LEO, YW, CMC, BSM, and MRF report no conflict of interest.

Funding

This work was supported, in part, by The Beef Checkoff. The funder had no role in designing, conducting, or reporting the research.

Data availability statement

All results described in the manuscript are provided in the Supplemental Material.