Red and Processed Meat Consumption and Risk for All-Cause Mortality and Cardiometabolic Outcomes A Systematic Review and Meta-analysis of Cohort Studies Dena Zeraatkar, MSc; Mi Ah Han, MD, PhD; Gordon H. Guyatt, MD, MSc; Robin W.M. Vernooij, PhD; Regina El Dib, PhD; Kevin Cheung, MD, MSc; Kirolos Milio, BSc; Max Zworth, BASc; Jessica J. Bartoszko, HBSc; Claudia Valli, MSc; Montserrat Rabassa, PhD; Yung Lee, BHSc; Joanna Zajac, PhD; Anna Prokop-Dorner, PhD; Calvin Lo, BHSc; Malgorzata M. Bala, PhD; Pablo Alonso-Coello, MD, PhD; Steven E. Hanna, PhD; and Bradley C. Johnston, PhD Background: Dietary guidelines generally recommend limiting intake of red and processed meat. However, the quality of evi- dence implicating red and processed meat in adverse health outcomes remains unclear. Purpose: To evaluate the association between red and pro- cessed meat consumption and all-cause mortality, cardiometa- bolic outcomes, quality of life, and satisfaction with diet among adults. Data Sources: EMBASE (Elsevier), Cochrane Central Register of Controlled Trials (Wiley), Web of Science (Clarivate Analytics), CINAHL (EBSCO), and ProQuest from inception until July 2018 and MEDLINE from inception until April 2019, without language restrictions, as well as bibliographies of relevant articles. Study Selection: Cohort studies with at least 1000 participants that reported an association between unprocessed red or pro- cessed meat intake and outcomes of interest. Data Extraction: Teams of 2 reviewers independently extracted data and assessed risk of bias. One investigator assessed cer- tainty of evidence, and the senior investigator confirmed the assessments. Data Synthesis: Of 61 articles reporting on 55 cohorts with more than 4 million participants, none addressed quality of life or satisfaction with diet. Low-certainty evidence was found that a reduction in unprocessed red meat intake of 3 servings per week is associated with a very small reduction in risk for cardiovascular mortality, stroke, myocardial infarction (MI), and type 2 diabetes. Likewise, low-certainty evidence was found that a reduction in processed meat intake of 3 servings per week is associated with a very small decrease in risk for all-cause mortality, cardiovascu- lar mortality, stroke, MI, and type 2 diabetes. Limitation: Inadequate adjustment for known confounders, re- sidual confounding due to observational design, and recall bias associated with dietary measurement. Conclusion: The magnitude of association between red and processed meat consumption and all-cause mortality and ad- verse cardiometabolic outcomes is very small, and the evidence is of low certainty. Primary Funding Source: None. (PROSPERO: CRD42017074074) Ann Intern Med. doi:10.7326/M19-0655 Annals.org For author affiliations, see end of text. This article was published at Annals.org on 1 October 2019. G rowing evidence shows an increased risk for cardio- metabolic disease associated with the consumption of red and processed meat. Although previous systematic reviews reported positive associations between red meat intake and all-cause mortality (1), cardiovascular mortality (2), and stroke (3) and between processed meat con- sumption and all-cause mortality (1, 4), cardiovascular mortality (2), stroke (3), coronary heart disease (5), and type 2 diabetes (5), results have not been consistent. One review did not find an association between unprocessed red meat and all-cause mortality (4), and another found no association with cardiovascular disease (5). Although Aune and colleagues (6) reported a relationship between red meat intake and type 2 diabetes, Micha and col- leagues (5) did not detect this association in a review pub- lished 1 year later. Methodological limitations in previous reviews in- cluded failure to address risk of bias of primary studies (for example, references 3 and 6), lack of evaluation of certainty of evidence (for example, references 2 to 6), and failure to consider the magnitude of observed ef- fect (for example, references 2 to 6). These limitations may have affected the credibility of recommendations issued by governments and authoritative organizations regarding red and processed meats. As part of NutriRECS (Nutritional Recommenda- tions and accessible Evidence summaries Composed of Systematic reviews), a new initiative to establish trust- worthy dietary recommendations that meet internation- ally accepted standards for guideline development, we developed guidelines addressing red and processed meat consumption (7). To inform these recommenda- tions, we conducted 5 systematic reviews of the evi- dence (8 –11). Here, we present results from a system- atic review of cohort studies addressing the association between red and processed meat consumption and all- cause mortality, cardiometabolic outcomes, quality of life, and satisfaction with diet among adults. See also: Related articles Editorial comment Web-Only Supplement Annals of Internal Medicine REVIEW Annals.org Annals of Internal Medicine © 2019 American College of Physicians 1 Downloaded from https://annals.org by McMaster University user on 10/01/2019