LAUSR

Higher red meat intake is associated with increased risk of cardiometabolic diseases, but causation of this relationships is unclear. This umbrella systematic review qualitatively assessed causality between red meat intake and cardiometabolic diseases. Two researchers independently screened and crosschecked 524 articles from MEDLINE, Scopus, Cochrane Library, and CINAHL up to November 25,2019. Articles included were systematic reviews and meta-analyses of observational or experimental studies using healthy subjects aged 19+ years; included red meat (RM) intake [total (TRM), unprocessed (URM), or processed (PRM)] as an a priori independent variable; and reported outcomes or risk factors of cardiovascular diseases (CVD) or type 2 diabetes mellitus (T2D). Causality was assessed using Bradford Hill's Causation Criteria: 1) strength (relative risk, RR ≥1.2), 2) consistency (≥67% of assessments), 3) specificity, 4) temporality, 5) biological dose-response gradient 6) plausibility, 7) coherence, 8) experimental evidence and 9) analogy. In total, 22 articles (16 with CVD data; 11 with T2D data) were included. While TRM and URM were statistically positively associated with CVD incidence and mortality, these associations were consistently weak (RR < 1.2). The strength of positive associations between TRM and T2D incidence were inconsistent while the positive associations between URM and T2D incidence were consistently weak. Results from short-term randomized controlled trials assessing effects of TRM and URM on CVD and T2D risk factors were predominately null. These experimental findings indicate a lack of coherence and need for more research to determine causality of the positive associations described above. For both CVD and T2D, temporality was established with the inclusion of prospective study designs. Researchers have proposed plausible biological mechanisms and analogies but specificity is lacking. Insufficient data precluded assessing causality between PRM and CVD or T2D; research is needed. Weakness of associations between total and unprocessed red meat intake and cardiometabolic diseases and lack of coherence with short-term experimental evidence on cardiometabolic disease risk factors reduces confidence that associations are causal. The Beef Checkoff.