Red and processed meat intakes and cardiometabolic disease: an umbrella systematic review and assessment of causal relations 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: N/A
Citation: N/A

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 increase risk for cardiometabolic diseases, but this research limits causal inference. We applied Bradford Hill’s Causality Criteria to evaluate potential for causal relationships between intakes of red and processed meat and cardiovascular diseases (CVD) or type 2 diabetes mellitus (T2DM) via an umbrella review of systematic reviews and meta-analyses of both observational and experimental research. Two researchers independently screened and crosschecked 605 articles using four databases from inception to July 2021. Selected reviews included studies among adults with a mean age =19 years; included unprocessed red meat (URM), processed meat (PM), or mixed URM+PM intake as an independent exposure or variable; and reported CVD or T2DM outcomes. Causality was inferred using Bradford Hill’s Causality Criteria. This review was registered in PROSPERO (CRD42020127976). Twenty-nine articles were included in this umbrella systematic review. Observational assessments of all three meat types and CVD outcomes consistently reported RRs <1.2, while the PM and Mixed URM+PM and T2DM outcome assessments consistently reported RRs =1.2. Evidence was insufficient for an association between URM and T2DM. Experimental assessments of Mixed URM+PM on CVD and T2DM risk factors were predominately null which lacked coherence with observational findings. For all meat types and CVD and T2DM outcomes, temporality was established and plausible mechanisms exist, but specificity and analogous relationships do not support a causal relation. These results suggest that red and processed meat intakes are not likely causally related to CVD. There is potential for a causal relationship between red meat and processed meat intakes and T2DM yet more experimental research is needed to further support this inference.