Cancer is the second-leading cause of death in the United States.1 So you might be surprised to learn that about one-third of cases could likely be prevented with diet and nutrition.2-4 

Decades of research suggest that the best diet for cancer prevention is eating foods that grow from the ground.3 That means lots of fruits, vegetables, grains, nuts, and legumes, and little to no meat or other animal products.5,6

In one study, researchers asked 70,000 volunteers about their diets and tracked them over time. They found the lowest cancer rates among individuals who didn't eat meat.2

Which leads to the natural question: Are vegetarians more resistant to cancer because they don't eat meat or because of what they eat instead of meat? 

The impact of red and processed meats on cancer rates

A recent paper in the Annals of Internal Medicine made headlines with its claim that there isn't enough evidence to prove eating less red meat improves health.7 But before you add bacon to your burger, keep this in mind:  Several prominent nutrition scientists and health organizations criticized the study’s methods and findings.8,9 Critics also note that the study didn’t reveal that its lead author has past research ties to the meat and food industries.10

Countless studies over several decades continually show that reducing red meat consumption lowers the risk of cancer. In 2018, the American Institute for Cancer Research and the World Cancer Research Fund released an updated report stating that eating red meat is a “probable cause” of colorectal cancer. The report also concludes that consuming processed meat is a “convincing cause” of colorectal cancer.3

Red meat is defined as mammalian muscle meat, including beef, veal, pork, lamb, venison, bison, mutton, and goat. Processed meats are meats preserved by smoking, salting, curing, or adding preservatives. Sliced turkey, bologna, deli meats, bacon, ham, and hot dogs are examples of processed meats.11

The majority of research is based on studies showing a positive association between eating red or processed meat and developing colorectal cancer. In one study, researchers found that each additional 3.5 ounces of red meat a day raises the relative risk of colorectal polyps by two percent. Just half as much daily processed meat raised the risk by 29 percent.12

The scientific community doesn’t fully understand the mechanisms between eating red or processed meat and an increased risk of cancer. It’s thought that chemical compounds created when red meat is cooked are cancer-causing. In addition, N-nitroso compounds and polycyclic aromatic hydrocarbons are carcinogenic chemicals that form during the method of creating processed meats.11,12

How a plant based diet might help fight cancer

Plant based foods – fruits, vegetables, legumes, nuts, and whole grains – are packed with nutrition. And research shows that eating lots of them is linked with lower cancer rates.13,14 Plants produce many phytochemicals (literally, plant chemicals) that are antioxidants that protect cells from damage.13

In the study that tracked the diets of 70,000 people, those who didn’t eat any animal products – including fish, dairy, or eggs (vegans) – had the lowest rates of cancer.2 Next in line were individuals who avoid eating meat but do eat fish or foods that come from animals, like milk or eggs.2 It’s important to note that study participants diagnosed with cancer also had a higher body mass index, were less active, and were more likely to smoke.2

The cancer-fighting properties associated with eating plants could simply be that individuals who primarily eat plant based foods are less likely to be overweight – a known risk factor for some types of cancers.6

Another way plant based foods likely prevent cancer is by boosting fiber consumption. One study found that young women who ate the most fiber-rich diets were 25-percent less likely to have breast cancer later in life.15 Other research finds that each 10 grams of daily fiber could lower the risk of colorectal cancer by 10 percent.16

Have your meat and eat it, too (in moderation)

Not ready to give up meat? That’s okay. Going “cold turkey” isn’t for everyone. And just because you eat meat doesn’t mean you’re going to get cancer. The term "flexitarian" describes someone who eats mostly plant based foods, but occasionally eats meat, poultry, and fish.

To shift to a more plant based diet, try these tips from Mayo Clinic Healthy Living Program dietitian Angie Murad, RDN, LD.

  • Choose moderation. A good guideline is to eat no more than 12-18 ounces of red meat or processed meat a week. Three ounces is about the size of your palm.17
  • Experiment with meatless meals. Set a goal to try one new meat-free recipe each week. And there's more to "Meatless Monday" than alliteration. You are more likely to stick with a new healthy habit at the beginning of the week.17
  • Use beans for bulk. Decrease the overall amount of meat in some recipes by increasing the amount of beans, lentils, or vegetables. Bonus: Those types of foods fill more space on your plate, and people often eat with their eyes – so you don't feel like you're being deprived.17 
  • Treat meat like a condiment. Instead of using meat as a main dish, use just a little bit for flavor. Try cutting turkey bacon into very small pieces and sprinkle them over sautéed Brussels sprouts. You get the flavor in every bite without using much meat.17

A healthy diet can go a long way to prevent many health conditions, including cancer, heart disease, and diabetes. Not sure where to start? Many popular diets can hone your eating habits. The MIND diet emphasizes eating foods that impact brain health to slow cognitive decline.18 The Mediterranean diet is typically high in vegetables, fruits, whole grains, beans, nut and seeds, and olive oil. And the Dietary Approaches to Stop Hypertension (DASH) diet is an eating plan to lower or control high blood pressure. Your health-care professional can also help determine the best eating plan for your health.

References

  1. Cancer facts and figures 2019. American Cancer Society. https://www.cancer.org/research/cancer-facts-statistics/all-cancer-facts-figures/cancer-facts-figures-2019.html [Accessed Nov.12, 2019.]
  2. Tantamango-Bartley Y, Jaceldo-Siegl K, Fan J, et al. Vegetarian diets and the incidence of cancer in a low-risk population. Cancer Epidemiol Biomarkers Prev 2013;22(2):286-294.
  3. World Cancer Research Fund/American Institute for Cancer Research. Continuous update project expert report 2018. Diet, nutrition, physical activity and colorectal cancer. www.aicr.org/continuous-update-project/reports/colorectal-cancer-2017-report.pdf [Accessed Jan. 13, 2020]
  4. World Health Organization. Cancer prevention. https://www.who.int/cancer/prevention/en/ [Accessed Nov. 12, 2019.]
  5. Key T, Appleby P, Spencer E, et al. Cancer incidence in vegetarians: results from the European prospective investigation into cancer and nutrition (EPIC-Oxford). Am J Clin Nutr 2009;89(5):1620S-1626S. 
  6. Lanou A, Svenson B. Reduced cancer risk in vegetarians: An analysis of recent reports. Cancer Manag Res 2010;3:1-8. 
  7. Johnston B, Zeraatkar D, Han M, et al. Unprocessed red meat and processed meat consumption: Dietary guideline recommendations from the nutritional recommendations (NutriRECS) consortium. Ann Intern Med 2019;171:756-764. 
  8. Physicians group files federal petition against Annals of Internal Medicine over false red meat claim. Physicians Committee for Responsible Medicine. https://www.pcrm.org/news/news-releases/physicians-group-files-federal-petition-against-annals-internal-medicine-over [Accessed Dec. 30, 2019.]
  9. Kumar V. Experts warn red and processed meat still pose a cancer risk. American Institute for Cancer Research. https://www.aicr.org/press/press-releases/2019/experts-warn-red-and-processed-meat-still-pose-cancer-risk.html [Accessed Dec. 30, 2019.]
  10. Reiley L. Research group that discounted risks of red meat has ties to program partly backed by beef industry. The Washington Post. https://www.washingtonpost.com/business/2019/10/14/research-group-that-discounted-risks-red-meat-has-ties-program-partly-backed-by-beef-industry/ [Accessed Dec. 30, 2019.]
  11. World Health Organization. Q & A on the carcinogenicity of the consumption of red meat and processed meat. www.who.int/features/qa/cancer-red-meat/en/ [Accessed Dec. 30, 2019]
  12. Aune D, Chan D, Vieira A, et al. Red and processed meat intake and risk of colorectal adenomas: A systematic review and meta-analysis of epidemiological studies. Cancer Causes Control 2013; doi:10.1007/s10552-012-0139-z.
  13.  Zhang Y, Gan R, Li S, et al. Antioxidant phytochemicals for prevention and treatment of chronic diseases. Molecules 2015; doi:10.3390/molecules201219753.
  14. Melina V, Craig W, Levin S. Position of the academy of nutrition and dietetics: Vegetarian diets. J Acad Nutr Diet 2016;116(12):1970-1980. 
  15. Farvid M, Eliassen H, Cho E, et al. Dietary fiber intake in young adults and breast cancer risk. Pediatrics 2016;137(3):e20151226  https://doi.org/10.1542/peds.2015-1226.
  16. Aune D, Chan D, Lau R, et al. Dietary fibre, whole grains, and risk of colorectal cancer: Systematic review and dose-response meta-analysis of prospective studies. BMJ 2011; doi: 10.1136/bmj.d6617.
  17. Murad A. (expert opinion). Mayo Clinic. Sept. 24, 2019.
  18. Morris M, Tangney C, Wang Y, et al. MIND diet slows cognitive decline with aging. Alzheimers Dement 2015;11(9):1015-1022.