Something that scores at least a "B" on the AFP Strength of Recommendation Taxonomy (SORT) would be a good start.
https://www.aafp.org/pubs/afp/authors/ebm-toolkit.html?cmpid...
So far the studies that appear to show a correlation between meat consumption and negative health outcomes have all been barely a step above junk science. We're talking about observational studies with poor controls (healthy subject effect), multiple uncontrolled variables, and small effect sizes.