there is something called "healthy user bias" that confounds these epidemiological studies.

namely in a society in which it is believed that meat is unhealthy and vegetables are healthy those who are health conscious will eat vegetables and those who are not will eat meat and the result will be that vegetarians will live longer than meat eaters simply because they are more health focused overall.

by contrast if you look at different cultures / nations ( as opposed to different individuals within same nation / culture ) then Koreans eat the most meat ( they eat dogs too ) and live the longest ...