Unprocessed Red Meat and Processed Meat Consumption: Dietary Guideline Recommendations From the Nutritional Recommendations (NutriRECS) Consortium

Contemporary dietary guidelines recommend limiting consumption of unprocessed red meat and processed meat. For example, the 20152020 Dietary Guidelines for Americans recommend limiting red meat intake, including processed meat, to approximately 1 weekly serving (1). Similarly, United Kingdom dietary guidelines endorse limiting the intake of both red and processed meat to 70 g/d (2), and the World Cancer Research Fund/American Institute for Cancer Research recommend limiting red meat consumption to moderate amounts and consuming very little processed meat (3). The World Health Organization International Agency for Research on Cancer has indicated that consumption of red meat is probably carcinogenic to humans, whereas processed meat is considered carcinogenic to humans (4). These recommendations are, however, primarily based on observational studies that are at high risk for confounding and thus are limited in establishing causal inferences, nor do they report the absolute magnitude of any possible effects. Furthermore, the organizations that produce guidelines did not conduct or access rigorous systematic reviews of the evidence, were limited in addressing conflicts of interest, and did not explicitly address population values and preferences, raising questions regarding adherence to guideline standards for trustworthiness (59). A potential solution to the limitations of contemporary nutrition guidelines is for an independent group with clinical and nutritional content expertise and skilled in the methodology of systematic reviews and practice guidelines, methods that include careful management of conflicts of interest, to produce trustworthy recommendations based on the values and preferences of guideline users. We developed the Nutritional Recommendations (NutriRECS) (7) international consortium to produce rigorous evidence-based nutritional recommendations adhering to trustworthiness standards (1012). To support our recommendations, we performed 4 parallel systematic reviews that focused both on randomized trials and observational studies addressing the possible impact of unprocessed red meat and processed meat consumption on cardiometabolic and cancer outcomes (1316), and a fifth systematic review addressing people's health-related values and preferences related to meat consumption (17). On the basis of these reviews, we developed recommendations for unprocessed red meat and processed meat consumption specific to health outcomes. Methods Guideline Development Process We developed our recommendations by following the NutriRECS guideline development process (7), which includes use of GRADE (Grading of Recommendations, Assessment, Development and Evaluation) methodology (1820). To inform our guideline recommendations, systematic reviews were conducted on the basis of a priori methods (21, 22). Guideline Team Structure This work involved 3 teams: 1. A core NutriRECS leadership team was responsible for supervision and coordination of the project and for drafting of the research questions, guideline protocol, and manuscripts. 2. A guideline panel included experts in health research methodology, nutritional epidemiology, dietetics, basic and translational research, family medicine, and general internal medicine. The panel included 3 members from outside the medical and health care communities. Panelists resided in high-income countries (Canada, England, Germany, New Zealand, Poland, Spain, and the United States). 3. A literature review team drafted the protocols for the systematic reviews, completed the literature search and eligibility review, abstracted data and conducted data analysis, and produced narrative and tabular summaries of the results. Framework for Panel Construction and Guideline Recommendations The core leadership team applied safeguards against competing interests (7). After generating a list of potential panel members without perceived vested interests, we contacted prospective candidates from North America, Western Europe, and New Zealand. Those who expressed interest completed a detailed form enumerating potential financial or intellectual conflicts during the previous 3 years. If important competing issues were identified (1 interested individual had financial conflicts), the potential panelist was not invited to participate. The Appendix Table shows a summary of the authors' conflict of interest forms; a full list of competing interests is available upon request from Dr. Johnston. Appendix Table. Summary of Panelists' Potential Conflicts of Interest Before our initial guideline panel meeting, the methods editor and panel chair contacted panelists, shared the draft questions, and received and incorporated feedback. At the initial meeting, the guideline panel discussed the scope of the project and agreed on the research questions and subgroups of interest. The panel focused on health outcomes thought to be associated with consumption of unprocessed red meat and processed meat and chose not to consider animal welfare and environmental issues related to meat consumption in making recommendations. The panel chose to exclusively focus on health outcomes because environmental and animal welfare concerns are very different issues that are challenging to integrate with health concerns, are possibly more societal than personal issues, and vary greatly in the extent to which people find them a priority. Finally, to consider these issues rigorously would require systematic reviews that we were not resourced to undertake. The panel also chose to make separate recommendations for unprocessed red meat and processed meat, given the potential for differential health effects and differing values and preferences of members of the public with regard to consumption of unprocessed meat versus processed meat. Target Audience for Recommendations The target audience for our guidance statement was individuals who consume unprocessed red meat or processed meat as part of their diet. The panel took the perspective of individual decision making rather than a public health perspective. Key Principles for PICO Questions and Study Eligibility Criteria Each NutriRECS project addresses a single nutrition question or topic, in this case guidance regarding the potential harms, benefits, and health-related values and preferences related to consuming unprocessed red meat and processed meat. We conducted a series of systematic reviews to inform our recommendations, addressing the following questions: 1) Among adults, what is the effect of diets and dietary patterns lower in red or processed meat versus diets higher in red or processed meat intake on the risk for outcomes important to community members? and 2) What are their health-related values and preferences for red and processed meat consumption? The panel considered all-cause mortality, major cardiometabolic outcomes (cardiovascular mortality, stroke, myocardial infarction, and diabetes), cancer incidence and mortality (gastrointestinal, prostate, and gynecologic cancer), quality of life, and willingness to change unprocessed red or processed meat consumption as critically important for developing recommendations. Important outcomes included surrogate outcomes (weight, body mass index, blood lipids, blood pressure, hemoglobin, anemia) and reasons for eating unprocessed red meat and processed meat. Methods for Systematic Reviews In consultation with an expert librarian, we searched the major literature databases to identify all relevant studies on harms, benefits, and health-related values and preferences regarding unprocessed red meat and processed meat. Each database was searched from inception until July 2018 without restrictions on language or date of publication, with MEDLINE searched through to April 2019 (see the systematic reviews in this issue [1317]). For harms and benefits, we included any randomized trial, as well as cohort studies including 1000 or more adults, that assessed diets with varying quantities of unprocessed red meat (for example, as servings or times/wk, or g/d) or processed meat (meat preserved by smoking, curing, salting, or addition of preservatives) (23) for a duration of 6 months or more. Studies in which more than 20% of the sample was pregnant or had cancer or a chronic health condition, other than cardiometabolic disease, were excluded. The review articles report our methods for screening, data abstraction, risk of bias assessment, and data analysis (1317). Panelists considered 3 servings per week as a realistic reduction in meat consumption (for example, moving from 7 to 4 servings, or 4 to 1 serving) on the basis of the average intake of 2 to 4 servings per week in North America and Western Europe (2428). We therefore framed the evidence regarding the potential reduced risks associated with a decrease of 3 servings per week of both unprocessed red meat and processed meat. We used GRADEpro software to formulate GRADE summary of findings tables for each PICO (population, intervention, control, and outcomes) question (29). The overall certainty of evidence was evaluated by using the GRADE approach (18). For estimates of risk with current levels of meat consumption, we used population estimates from the Emerging Risk Factors Collaboration study for cardiometabolic outcomes (30) and population estimates from GLOBOCAN for cancer outcomes (31). Using these resources, we based our estimates for cardiometabolic mortality and incidence outcomes on an average of 10.8 years of follow-up, whereas for cancer mortality and incidence, our estimates are for the overall lifetime risk. Complementing existing GRADE standards and to determine whether we should rate up for a doseresponse effect, we assessed the plausibility of a causal relationship between meat and adverse health outcomes by contrasting results from 2 bodies of evidence (7, 22): cohort studies specifically addressing red meat and processed meat intake, and cohort studies addressing dietary patte