A review of six studies that evaluated the effects of meat and vegetarian diets on mortality involving more than 1.5 million people concluded all-cause mortality is higher for those who eat meat, particularly red or processed meat, on a daily basis.
The work by physicians from Mayo Clinic in Arizona published in the Journal of the American Osteopathic Association helps to affirm claims by the United Nations International Agency for Research on Cancer (IARC) claim that meat is a carcinogen as dangerous as plutonium or cigarette smoking. Despite variability in the data, they still conclude that increased intake of red meat, especially processed red meat, is associated with increased all-cause mortality.
While findings for U.S. and European populations differed somewhat, they found the steepest rise in mortality at the smallest increases of intake of total red meat. That 2014 study followed more than one million people over 5.5 to 28 years and considered the association of processed meat (such as bacon, sausage, salami, hot dogs and ham), as well as unprocessed red meat (including uncured, unsalted beef, pork, lamb or game).
A 2014 meta-analysis examined associations with mortality from cardiovascular disease and ischemic heart disease. In that study of more than 1.5 million people, researchers found only processed meat significantly increase the risk for all-cause mortality.
Combined, the findings of these studies are statistically significant in their similarity, the reviewers noted. Further, a 2003 review of more than 500,000 participants found a decreased risk of 25 percent to nearly 50 percent of all-cause mortality for very low meat intake compared with higher meat intake.
They also found a 3.6-year increase in life expectancy for those on a vegetarian diet for more than 17 years, as compared to short-term vegetarians.