Researchers followed 536,000 men and women, ages 50 to 71, for an average 16 years and found that those who ate the most meat from mammals and processed meat had a 26 percent greater risk of dying within the study period than those who ate the least (Brit Med J, May 9, 2017). High mammal meat consumption was associated with increased rates of death from cancer, heart disease, respiratory disease, stroke, diabetes, infections, kidney disease and liver disease. The authors report no support or influence from industry. The study was supported by the U.S. National Institutes of Health (NIH) and the National Cancer Institute (NCI).
Those who ate the highest proportion of poultry and fish had a 25 percent reduced risk of dying. The authors propose that the heme iron in mammal meats and nitrates in processed meats may be the factors that explain the higher rates of death. Heme iron and nitrates are both potent oxidants that are associated with DNA damage and increased risk for cancers. The authors believe that apparent benefit of eating fish and poultry is that they contain much lower amounts of heme iron and nitrates. Many earlier studies also show that eating mammal meat daily is associated with higher death rates (Am J Clin Nutr, Sept 2014;100(3):924-9; Am J Epidemiol, Feb 1, 2014;179(3):282-9).
Peripheral Artery Disease: Eating meat from mammals is associated with increased risk for peripheral artery disease, blockage of arteries leading to the arms, legs, head and belly (Am J Clin Nutr, Jan 12, 2017
Cancer: An extensive review of retrospective and prospective studies showed that mammal meat increases cancer risk (British Medical Bulletin, Dec 23, 2016). Beef, pork, lamb and other meats from mammals may cause cancers of the colon, prostate or pancreas (The Lancet Oncology, 2015;16(6):1599-1600).
Breast Cancer: Women who eat grilled, barbecued or smoked meats are at increased risk for developing breast cancer, and continuing to eat mammal meat after breast cancer diagnosis increases risk of dying from breast cancer. (Nutr Cancer, 2009; 61(4):437–446; J Natl Cancer Inst, Jan 4, 2017;109(6):djw299).
Colon Cancer: Eating meat is associated with increased risk of colon cancer, and processing the meat increases risk (European Journal of Nutrition, Nov 24, 2016). The World Health Organization’s International Agency for Research on Cancer issued a report that eating processed meats (bacon, sausage, bologna, hot dogs and so forth) raises risk for colon cancer. Many articles show that mammal meat is associated with increased risk for colon cancer (Am Coll Nutr, 2015;34(6):521-543), and the more meat that you eat, the greater your risk (Public Health Nutr, published online July 6, 2015). On the other hand, taking at least two ounces of tree nuts but not peanuts) a week reduced colon cancer recurrence for patients who had metastatic colon cancer (American Society of Clinical Oncology Annual Meeting, Chicago, June 2017).
Diabetes: A study from the University of Eastern Finland showed that eating animal protein increases, and plant protein decreases, risk for diabetes and that replacing animal protein with plant protein reduces diabetes risk (British Journal of Nutrition, April 11, 2017). This confirmed the same findings by other researchers (Circulation, Feb 12, 2008;117(6):754-61).
I believe that everyone should eat lots of fruits, vegetables, unground whole grains, beans seeds and nuts. Of course, if you are allergic to or have a specific reaction to certain plants, you should avoid those plants. I recommend avoiding or restricting meat from mammals, based on the studies cited above and many others; see Why I Still Restrict Meat.