Researchers at the Centre for Ecological Research in Hungary analyzed the death records for 110,148 animals from 191 mammal species that died in zoos and found that carnivorous mammals were much more likely to die of cancer than mammals that rarely or never eat animals (Nature, 2022; 601(7892): 263–267).
Humans are mammals, so we might expect to see similar results in studies of human diets. The Golestan cohort study followed 50,045 people aged 40-75 in northeastern Iran, where the people eat more than four times as much chicken as mammal meat (pork, beef and lamb). The more mammal meat, organ meat, and processed meat they ate, the more likely they were to develop stomach cancer (Int J Cancer, Oct 1, 2022;151(7):1005-1012). The women who ate mammal meat were at increased risk for esophageal cancer also. Another study found that eating mammal meat was associated with an increased risk of colorectal cancer, while chicken and turkey were not associated with increased risk (Front Nutr, 2023 Feb 13;10:1078963). The data were corrected for body weight and cholesterol.
Colon Cancer Risk
A review of 45 prospective studies found that risk for suffering colon cancer is increased by drinking alcohol and eating red meat, and decreased by eating more fiber (JAMA Netw Open, Feb 16, 2021;4(2):e2037341). Many studies associate eating mammal meats with increased colon cancer risk (Colorectal Cancer 2011 Rep Lond WCRF/AICR, 2011:1-40). A prospective study of 32,147 women followed for an average 17.2 years found that avoiding red meat was associated with a statistically significant decreased risk for distal colon cancer and a non-statistically significant decreased risk for total colon cancer (International Journal of Cancer, April 1, 2018). A prospective study of Seventh Day Adventists found that people who ate fish and avoided red meat had a reduced risk for colon cancer (JAMA Intern Med, 2015;175:767-76). Those who ate meat regularly had a higher risk for colon cancer than those who ate fish and no meat, or those who ate meat less than once a week (Sci Rep, 2015;5:13484). The World Health Organization (WHO) reported that eating processed meat and red meat increased risk of colorectal cancer (J Gastroenterol, Dec 2, 2016; Br Med Bull, Dec 23, 2016; J Hum Nutr Diet, Jun 14, 2016; Br Med Bull, Dec 18, 2016).
More than 1.3 million North Americans have had colorectal cancer. Colon cancer is associated with lifestyle factors that cause harmful bacteria called Fusobacterium (Front Oncol, Oct 15, 2018; 8:371) to thrive in your colon, which include:
• Excess weight: Colon cancer is far more common in people who are overweight, a major risk factor for having high blood sugar levels and diabetes. Obese people have different bacteria in their colons than skinny people do (Nature, 2009;457:480-484). Gaining excess weight is associated with having certain colon bacteria that increase the absorption of more calories from your colon (Nature, 2006;444:1027-1031). See How Gut Bacteria Affect Weight. People with markers of high blood sugar called metabolic syndrome are at more than double the risk of developing colon cancer (Cancer Epidemiology, Biomarkers & Prevention , Feb, 2017). Eating sugar added foods and red meat may increase colon cancer risk by creating a fatty liver that causes high blood sugar levels (J Hepatol, Mar 19, 2018).
• Lack of Exercise: A prospective study of 226,584 participants over age 45 found that both being overweight and not having an exercise program are independent risk factors for colon cancer (BMC Public Health, March 6, 2018). Other studies show that sitting more than 11 hours each day is associated with increased colon cancer risk (Br J Cancer, Mar 3, 2015;112(5):934-942). Exercising regularly reduces an overweight person’s chances of developing colon cancer (Med Sci Sports Exerc, 2002;34(6):913-9). Exercising regularly also reduces colon cancer risk in people who sit for long periods each day (Lancet 2016;388(10051):1302-10; Cancer Epidemiol Biomark Prev, 2010;19(11):2691-709).
The same lifestyle habits that increase risk for heart attacks also increase risk for obesity, diabetes and certain cancers, particularly colon cancer. All of the risk factors for colon cancer are associated with increased numbers of harmful bacteria in the colon. You can reduce your risk for colon cancer by:
• avoiding or limiting red meat and processed meats, fried foods, sugar-added foods and drinks with sugar in them
• avoiding smoke and alcohol
• maintaining a healthful weight
• exercising regularly