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

Authors: HILL, ERICA - Purdue University; O'Connor, Lauren; WANG, YU - Purdue University; CLARK, CAROLINE - Purdue University; MCGOWAN, BETHANY - Purdue University; FORMAN, MICHELE - Purdue University; CAMPBELL, WAYNE - Purdue University

Submitted to: Critical Reviews in Food Science and Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2022
Publication Date: 9/26/2022
Citation: Hill, E.R., O'Connor, L.E., Wang, Y., Clark, C.M., Mcgowan, B.S., Forman, M.R., Campbell, W.W. 2022. Red and processed meat intakes and cardiovascular disease and type 2 diabetes mellitus: an umbrella systematic review and assessment of causalrelations using Bradford Hill’s criteria. Critical Reviews in Food Science and Nutrition. 64(9):2423-2440. https://doi.org/10.1080/10408398.2022.2123778.
DOI: https://doi.org/10.1080/10408398.2022.2123778

Interpretive Summary: The 2020-2025 Dietary Guidelines for Americans recommends eating patterns that are low in ‘red and processed meat intake’ with the caveat that ‘lean meats’ can be part of a healthy eating pattern (as mainly fresh, frozen or canned versus further processed) when recommendations for sodium and saturated fat intakes are met. Our current dietary recommendations are based largely on associations, with limited understanding of causality. The Bradford Hill Causality Criteria were developed to infer the potential for causal relations of public health concern. The objective of this umbrella systematic review is to apply the Bradford Hill Causality Criteria to infer the potential for causal relations between intakes of red and processed meat and cardiovascular disease or type 2 diabetes mellitus using systematic reviews and meta-analyses of both observational and experimental research on the topic. Twenty-nine articles were included in this umbrella systematic review. We infer processed meat and mixed red and processed meat intakes are not causally related to cardiovascular disease outcomes but potentially causally related to type 2 diabetes mellitus due to consistently strong associations. Type 2 diabetes mellitus is a major risk factor for cardiovascular disease, so the potential causal relation between red and processed meats and type 2 diabetes mellitus could indirectly affect cardiovascular disease outcomes.

Technical 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.