I thought this was already well-established, but for for the skeptics out there, this is one of the largest and most comprehensive studies to date on meat consumption and mortality (death rate) from disease. The study, "Meat Intake and Mortality: A Prospective Study of Over Half a Million People," was published in the esteemed journal Archives of Internal Medicine this month. Click here for the full abstract.
UPDATE 5/5/09: Jane Brody published a really well-written story on this in the New York Times -- take a look.
Investigators studied a half a million people aged 50 to 71 (at the outset), looking at their diets and their ultimate causes of death. They specifically were looking for a connection between intakes of different types of meat (red, white, and processed) and risk of cause-specific mortality (meaning, which diseases did they get that led to their deaths?).
Over ten years, deaths and their causes were recorded. The main finding was that the higher the red meat and processed meat intake, the greater the risk of dying from cancer, heart disease, and just dying in general.
Interestingly, white meat consumption was not shown to have any association with these risks, but that certainly does not mean that the fountain of youth is hidden in your McNuggets. Certainly red and processed meats contain more saturated and trans fat than white, and that can explain at least part of these results. I am skeptical that white meat is in any way protective -- I have noticed in general that people who eat a lot of poultry also eat lots of salads and vegetables, so this may account for the lack of association. Whatever the explanation, no study has ever shown an increased risk of death or disease from including more vegetables, fruits, whole grains, and beans, so vegans still have the best competitive edge.