Dietary guidelines generally recommend limiting intake of red and processed meat. However, the quality of evidence implicating red and processed meat in adverse health outcomes remains unclear. To evaluate the association between red and processed meat consumption and all-cause mortality, cardiometabolic outcomes, quality of life, and satisfaction with diet among adults. 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. Cohort studies with at least 1000 participants that reported an association between unprocessed red or processed meat intake and outcomes of interest. Teams of 2 reviewers independently extracted data and assessed risk of bias. One investigator assessed certainty of evidence, and the senior investigator confirmed the assessments. 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, cardiovascular mortality, stroke, MI, and type 2 diabetes. Inadequate adjustment for known confounders, residual confounding due to observational design, and recall bias associated with dietary measurement. The magnitude of association between red and processed meat consumption and all-cause mortality and adverse cardiometabolic outcomes is very small, and the evidence is of low certainty. None. (PROSPERO: CRD42017074074)

Cancer incidence has continuously increased over the past few centuries and represents a major health burden worldwide. To evaluate the possible causal relationship between intake of red and processed meat and cancer mortality and incidence. Embase, Cochrane Central Register of Controlled Trials, Web of Science, CINAHL, and ProQuest from inception until July 2018 and MEDLINE from inception until April 2019 without language restrictions. Cohort studies that included more than 1000 adults and reported the association between consumption of unprocessed red and processed meat and cancer mortality and incidence. Teams of 2 reviewers independently extracted data and assessed risk of bias; 1 reviewer evaluated the certainty of evidence, which was confirmed or revised by the senior reviewer. Of 118 articles (56 cohorts) with more than 6 million participants, 73 articles were eligible for the dose–response meta-analyses, 30 addressed cancer mortality, and 80 reported cancer incidence. Low-certainty evidence suggested that an intake reduction of 3 servings of unprocessed meat per week was associated with a very small reduction in overall cancer mortality over a lifetime. Evidence of low to very low certainty suggested that each intake reduction of 3 servings of processed meat per week was associated with very small decreases in overall cancer mortality over a lifetime; prostate cancer mortality; and incidence of esophageal, colorectal, and breast cancer. Limited causal inferences due to residual confounding in observational studies, risk of bias due to limitations in diet assessment and adjustment for confounders, recall bias in dietary assessment, and insufficient data for planned subgroup analyses. The possible absolute effects of red and processed meat consumption on cancer mortality and incidence are very small, and the certainty of evidence is low to very low. None. (PROSPERO: CRD42017074074)

Few randomized trials have evaluated the effect of reducing red meat intake on clinically important outcomes. To summarize the effect of lower versus higher red meat intake on the incidence of cardiometabolic and cancer outcomes in adults. EMBASE, CENTRAL, CINAHL, Web of Science, and ProQuest from inception to July 2018 and MEDLINE from inception to April 2019, without language restrictions. Randomized trials (published in any language) comparing diets lower in red meat with diets higher in red meat that differed by a gradient of at least 1 serving per week for 6 months or more. Teams of 2 reviewers independently extracted data and assessed the risk of bias and the certainty of the evidence. Of 12 eligible trials, a single trial enrolling 48 835 women provided the most credible, though still low-certainty, evidence that diets lower in red meat may have little or no effect on all-cause mortality (hazard ratio [HR], 0.99 [95% CI, 0.95 to 1.03], cardiovascular mortality (HR, 0.98 [CI, 0.91 to 1.06]), and cardiovascular disease (HR, 0.99 [CI, 0.94 to 1.05]). That trial also provided low- to very-low-certainty evidence that diets lower in red meat may have little or no effect on total cancer mortality (HR, 0.95 [CI, 0.89 to 1.01]) and the incidence of cancer, including colorectal cancer (HR, 1.04 [CI, 0.90 to 1.20]) and breast cancer (HR, 0.97 [0.90 to 1.04]). There were few trials, most addressing only surrogate outcomes, with heterogeneous comparators and small gradients in red meat consumption between lower versus higher intake groups. Low- to very-low-certainty evidence suggests that diets restricted in red meat may have little or no effect on major cardiometabolic outcomes and cancer mortality and incidence. None (PROSPERO: CRD42017074074).

Polyphenols might have a role in the prevention of several chronic diseases, but evaluating total dietary polyphenol (TDP) intake from self-reported

A person's meat consumption is often determined by their values and preferences. To identify and evaluate evidence addressing health-related values and preferences regarding meat consumption. MEDLINE, EMBASE, Web of Science, Centre for Agriculture and Biosciences Abstracts, International System for Agricultural Science and Technology, and Food Science and Technology Abstracts were searched from inception to July 2018 without language restrictions. Pairs of reviewers independently screened search results and included quantitative and qualitative studies reporting adults' health-related values and preferences regarding meat consumption. Pairs of reviewers independently extracted data and assessed risk of bias. Data were synthesized into narrative form, and summaries were tabulated and certainty of evidence was assessed using the GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach. Of 19 172 initial citations, 41 quantitative studies (38 addressed reasons for meat consumption and 5 addressed willingness to reduce meat consumption) and 13 qualitative studies (10 addressed reasons for meat consumption and 4 addressed willingness to reduce meat consumption) were eligible for inclusion. Thirteen studies reported that omnivores enjoy eating meat, 18 reported that these persons consider meat an essential component of a healthy diet, and 7 reported that they believe they lack the skills needed to prepare satisfactory meals without meat. Omnivores are generally unwilling to change their meat consumption. The certainty of evidence was low for both “reasons for meat consumption” and “willingness to reduce meat consumption in the face of undesirable health effects.” Limited generalizability of findings to lower-income countries, low-certainty evidence for willingness to reduce meat consumption, and limited applicability to specific types of meat (red and processed meat). Low-certainty evidence suggests that omnivores are attached to meat and are unwilling to change this behavior when faced with potentially undesirable health effects. None. (PROSPERO: CRD42018088854)

Polyphenols have beneficial effects on several chronic diseases but assessing polyphenols intake from self-reported dietary questionnaires tends to be inaccurate and not very reliable. A promising alternative is to use urinary excretion of polyphenols as a proxy measure of intake. The best method to assess urinary excretion is to collect 24-h urine. However, since collecting 24-h urine method is expensive, time consuming and may be difficult to implement in large population-based studies, measures obtained from spot urine normalized by creatinine are commonly used. The purpose of the study was to evaluate the correlation between polyphenols dietary intake and total urinary polyphenol excretion (TPE), expressed by both 24-h volume and urinary creatinine normalization in 928 participants from the InCHIANTI study. Dietary intake data were collected using a validated food frequency questionnaire. Urinary TPE was analyzed by Folin-Ciocalteau assay. Both urinary TPE expression models were statistically correlated (r=0.580), and the partial correlation coefficient improved (pr=0.722) after adjusting for the variables that modify the urinary creatinine excretion (i.e. gender, age, BMI, physical activity and renal function). In crude models, polyphenol intake was associated with TPE corrected by 24-h volume (r=0.211; P<0.001), but not with creatinine normalization (r=0.014; P=0.692). However, urinary TPE expressed by creatinine correction was significantly correlated with dietary polyphenols after adjusting for covariates (pr=0.113; P=0.002). We conclude that urinary TPE expressed by 24-h volume is a better biomarker of polyphenol dietary intake than by urinary creatinine normalization. After covariate adjustment, both can be used for studying the relationships between polyphenol intake and health in large-scale epidemiological studies.