Experts pretty much seem to agree that a predominately plant-based diet is the way to go for cancer prevention. However one of the biggest debates that still exists is whether or not meat and dairy contribute to cancer. Personally, I want to get to the root of this so that I can make an informed research-backed decision on what to eat.
For full transparency, I want you to know that as I am writing this I am eating a fully plant-based diet. This is mainly because the initial research I have done has thoroughly convinced me that a predominately plant-based diet is the most supported for cancer prevention. I also began seeing studies about the link between meat and dairy and cancer and decided to cut it out completely until I could review more research.
Am I an adamant vegan that is trying to convince people to stop eating meat? Not quite. Let’s get things straight. I love meat and dairy. I am a recovering cheese-a-holic. I could easily sit down and eat an entire block of sharp cheese. Cheese platter with six different cheeses to taste? Yes please. I easily can go without red meat and chicken, but I love wild game. I do love animals and believe that they should be treated in a humane way. I find factory farming practices gross and cruel, so when I was eating meat, I chose organic free range meat or wild game. The focus of this post is on the research around diet and cancer, not on how we should treat animals.
Why am I investigating this? To be clear, it is not because I feel deprived or because I don’t have enough good food to eat. I want to review the research from all angles so that I can be up to date on the current state of research and be an advocate for my own health. I don’t want to be swept into the latest fad diet and want to make informed decisions. I realize that just because something tastes good (like Doritos! mmm..), doesn’t mean eating it is good for me.
What does my intuition say? When I do research, I like to cross check it with what makes intuitive sense to me. For example, if I was stranded in the woods or on an island what would I eat? I would probably eat lots of plants and small amounts of small animals and seafood that I could catch. Maybe some larger animals on rare occasions. I probably wouldn’t be consuming dairy, and I wouldn’t be eating any processed meats or processed foods.
But that’s just my intuition, which could be wrong. Let’s dig in.
What type of diet do the major cancer organizations recommend?
The Word Cancer Research Fund International, American Institute for Research on Cancer, American Cancer Society, World Health Organization, International Agency for Research on Cancer, Mayo Clinic, MD Anderson Cancer Center, and The Society for Integrative Oncology all support the same recommendation:
Limit red meat intake, avoid processed meat, and eat more fruits, vegetables, whole grains, and beans (WCRF/AICR, 2007; Stewart et al, 2014).
Based on an extensive review of the research on diet and cancer the World Cancer Research Fund and the American Institute for Research on Cancer recommend eating mostly foods of plant origin (WCRF/AICR, 2007).
What is red meat? Beef, Bison, Pork, Lamb, Goat
What is processed meat? Meat that has been salted, cured, smoked, or has chemical preservatives added. This includes bacon (sorry!), salami, pastrami, ham, sausage, bratwursts, hot dogs, lunch meats, ready-to-eat meat products, among others.
But what does the research say?
Many of us have heard of laboratory studies linking meat and dairy to cancer, but what does the research say about humans who eat meat or dairy?
Luckily, there have been some recent large-scale studies which include analysis of diet and cancer risk. Let’s focus on these large-scale, long-term studies so that we don’t get derailed by one-off findings.
In 2007, The World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) led a thorough review of the current state of research on diet and cancer with an expert panel of cancer researchers. Their goal was to come up with clear conclusions and recommendations. I will refer to the findings in this report in the answers to many of the questions below.
The WCRF/AICR report used a scoring system of “Convincing”, “ Probable”, “Limited – Suggestive”, and “Unlikely” to rate whether different dietary factors increase or decrease risk of cancer. So Convincing is the highest level, and Unlikely is the lowest (WCRF/AICR, 2007)
Does processed meat cause cancer?
It is Convincing. The WCRF/AICR report concluded that an increased risk of colorectal cancer due to processed meat is “Convincing”, and an increased risk of esophagus, lung, stomach, and prostate cancer is “limited and suggestive” (WCRF/AICR, 2007).
A large-scale European study, The EPIC study (about 450,000 people), estimated from their research that 3% of all deaths could be prevented by reducing processed meat consumption to less than 20 grams per day (about 1 strip of bacon) (Rohrmann et al, 2013). Specifically, they found a positive association between processed meat consumption and risk of dying from cancer.
In the AARP study (600,000 people, diet and cancer study), they estimated this percentage to be even higher at about 20% reduction in death rates if women decreased processed meat consumption to less than 1.6grams per 1,000kcal of food consumed during each day (Sinha et al, 2009).
Does red meat cause cancer?
It is Convincing. The WCRF/AICR report concluded that an increased risk of colorectal cancer due to red meat is “Convincing”, and an increased risk of esophagus, lung, pancreas and endometrium cancer is “Limited – Suggestive” (WCRF/AICR, 2007).
The Health Professionals Follow-up Study (studied 37,000 people), found that high red meat intake was related to higher mortality rates (Pan et al, 2012). If people lowered their red meat consumption (processed and unprocessed) to less than 0.5 servings per day it was estimated that 7.6 percent of deaths could be prevented. The Nurses’ Health study (studied 83,000 people) reported that 9.3 percent of death could be prevented (Pan et al, 2012).
Do poultry and other white meat cause cancer?
Not sure. According to the WCRF/AICR report, there currently isn’t enough evidence to say one way or another(WCRF/AICR, 2007).
The AARP study found that cancer mortality rate went down with white meat intake (fish was included as white meat), however there was an increase of cardiovascular disease (Sinha et al, 2009). It was unclear if the decreased risk was due to the subjects eating less red meat in favor of white meat, or if there are benefits to eating white meat. For example, there was no comparison to a diet without meat compared to a diet with white meat.
The EPIC study did not find an association between poultry and cancer (Rohrmann et al, 2013). This does not include processed white meat which was included in the processed meat category above.
Does dairy cause cancer?
There is Limited – Suggestive evidence. The WCRF/AICR report found limited suggestive evidence that milk and dairy products increase the risk of prostate cancer, and that cheese increases risk of colorectal cancer. Diets high in calcium were found to be a “Probable” cause of prostate cancer (WCRF/AICR, 2007).
However, they also found that it was “probable” that milk decreases risk of colorectal cancer, and “limited-suggestive” evidence it decreases bladder cancer.
The EPIC study looked at 142,000 men and found that increased consumption of dairy protein was associated with a 32% increased risk of prostate cancer. They also found an association between dairy calcium and prostate cancer, but not with calcium from other food sources (Allen et al, 2008)
Do eggs cause cancer?
Not sure. According to the WCRF/AICR report, there currently isn’t enough evidence to say one way or another (WCRF/AICR, 2007).
But here is some interesting research..
In the Health Professionals Follow-up study it was shown that men with the highest choline counts (highest in eggs, meat, dairy) had a 70% increased risk of prostate cancer (Richman et al, 2012)
Another study followed 27,000 men over 14 years and found an 81% increase risk of getting lethal prostate cancer in the men who ate 2.5 or more eggs per week compared to 0.5 eggs per week (men did not have cancer at start of study) (Richman et al, 2011)
Additionally, a review paper that analyzed research papers (total of 424,000 people) on egg consumption and GI cancers found an increased risk of colon cancer with egg consumption (Tse et al, 2014)
Does fish cause cancer?
It’s a mixed bag. There is a “Probable” increased risk of nasopharynx cancer with cantonese-style salted fish (method of preserving fish). There is a “Limited-Suggestive” decrease in colorectal cancer with fish consumption (WCRF/AICR, 2007).
The WCRF/AICR study says “The balance of risks and benefits of eating fish at various stages of the life course needs to be determined.”
For example, much of fish is contaminated with mercury which is a neurotoxin and is classified as “possibly carcinogenic” by the International Agency on Cancer Research. To learn about the fish with the highest and lowest mercury levels, check out this pocket guide. Spoiler alert – Salmon is one of the lowest (though pick wild since farmed has high levels of pollutants), and Tuna has some of the highest mercury levels.
What about organic vs. non-organic?
While there is evidence that organic products contain fewer chemicals like pesticides, we still don’t know the effect on cancer risk (WCRF/AICR, 2007).
One study that followed 623,000 women over 9 years showed a weak association between non-Hodkin lymphoma and non-organic food but no links with other cancers (Bradbury et al 2014). In general, more long-term research studies are needed to come to a conclusion on the link between organic vs non-organic food and chronic disease (Baranski et al, 2017).
Potential reasons why?
Here are some potential reasons why some animal products are linked to cancer. Keep in mind, these are potential reasons and there need to be more large scale research studies to determine a definitive cause. These are not all-inclusive of every theory.
Cooking methods: Cooking meat at high temperatures causes carcinogens such as heterocyclic amines and polycyclic aromatic hydrocarbons to form on the surface of the meat (WCRF/AICR, 2007; Stewart et al, 2014).
Even chicken baked at 350 degrees F has significant build up of heterocyclic amines (Zaidi et al, 2012)
Fish and fried bacon have the highest levels of heat induce carcinogens and boiled meat appears to have the lowest levels (Puangsombat et al, 2012).
Excess animal protein (meat and dairy) promotes Insulin-Like Growth Factor (IGF1) which contributes to cancer growth (WCRF/AICR, 2007, Allen et al, 2002). IGF-1 levels have been linked with risk of breast cancer, prostate cancer, and the spread of cancer to other regions (Key et al, 2010; Rowlands et al, 2009; Zhang et al, 2010).
Continuing to drink milk beyond child years is unnatural and may promote growth of cancerous cells (Melnik et al, 2012)
Meat can react with bacteria in the gut, forming a carcinogen. Excess haem iron from animal meat reacts with bacteria in our stomachs and creates N-nitroso compounds which are carcinogenic. Free iron can also lead to oxidation, inflammation, and free radicals (WCRF/AICR, 2007; Stewart et al, 2014).
Nitrates in processed meats can also contribute to the production of N-nitroso (WCRF/AICR, 2007).
Veterinary drugs. Hormonal drugs are given to animals in order to prevent and terminate pregnancy and stimulate milk production (WCRF/AICR, 2007). Some of these hormones are known to be carcinogens. They are banned in the EU, but are still used in the US.
Viruses. Farmed animals are known to develop viruses which spread due to many of the farming practices. For example, a report from the USDA showed that 89% of cattle in the US are infected with Bovine Leukemia Virus. The virus should technically be mostly inactivated by pasteurization (the case for raw milk isn’t looking so good now… ), however it could potentially be in the meat of the animal.
Exposure to bovine leukemia virus has been linked to breast cancer, but this is an area of controversy and conflicting results (Buehring et al, 2015; Gillet et al, 2016).
Additionally, poultry workers are 9x more likely to develop pancreatic and liver cancer which is suspected to be due to poultry viruses (Felini et al, 2011).
Pollutants. Meat, fish, and dairy products contain industrial pollutants (for example, chemicals used in factories), some which are known carcinogens and others are potential carcinogens (Hernandez et al, 2015; Schecter et al, 2006; Huwe et al, 2011, Crinnion et al 2011). One study looked at the concentration of carcinogens in meat products and recommended the general public not surpass 5 servings of beef/pork/chicken in a month (Hernandez et al, 2015).
Turkey and fish have some of the highest levels of pollutants, with farmed salmon being the worst (10x’s the level of wild salmon) (Fernandes et al, 2010). These pollutants can stay in our bodies for many years (Crinnion et al, 2011)
As previously mentioned on the section about fish, many commonly consumed fish (like tuna) are highly contaminated with mercury which is rated as a possible carcinogen.
My conclusion and decision?
My overall observation was that many of the foods tied to cancer risk are linked to manmade interventions (processing, cooking methods, etc). It isn’t necessarily known if meat in it’s truest form is bad to eat, but it is very hard if not impossible to find meat like that these days.
I encourage everyone to make their own decision and interpret the research in their own way. What I personally decide to do with all of this information is my own choice. I would be more than happy to email you specifically what I am planning to eat after doing all of this research (you can request it below). I will also include pointers on how to explain it to other people.
I have learned that food choices have a lot of emotion behind them. I now tell people my choices only when they ask and when necessary!
Allen NE, et al. The Associations of Diet with Serum Insulin-like Growth Factor I and Its Main Binding Proteins in 292 Women Meat-Eaters, Vegetarians, and Vegans. Cancer Epidemiol Biomarkers Prev. 2002 Nov;11(11):1441-8.
Allen NE, et al. Animal foods, protein, calcium and prostate cancer risk: the European Prospective Investigation into Cancer and Nutrition. Br J Cancer. 2008;98(9):1574-81.
Barański M, et al. Effects of organic food consumption on human health; the jury is still out!. Food Nutr Res. 2017;61(1):1287333.
Bradbury KE, et al. Organic food consumption and the incidence of cancer in a large prospective study of women in the United Kingdom. Br J Cancer. 2014;110(9):2321-6.
Buehring GC, et al. Exposure to Bovine Leukemia Virus Is Associated with Breast Cancer: A Case-Control Study. PLoS One. 2015 Sep 2;10(9):e0134304.
Crinnion. The role of persistent organic pollutants in the worldwide epidemic of type 2 diabetes mellitus and the possible connection to Farmed Atlantic Salmon (Salmo salar). Altern Med Rev. 2011 16(4):301 – 313.
Felini M, et al. A pilot case-cohort study of liver and pancreatic cancers in poultry workers. Ann Epidemiol 2011 21(10):755 – 766.
Fernandes A, et al.Polychlorinated naphthalenes (PCNs): congener specific analysis, occurrence in food, and dietary exposure in the UK. Environ Sci Technol. 2010;44(9):3533-8.
Gillet NA,et al. Whole genome sequencing of 51 breast cancers reveals that tumors are devoid of bovine leukemia virus DNA. Retrovirology. 2016;13(1):75.
Hernández ÁR, et al. An estimation of the carcinogenic risk associated with the intake of multiple relevant carcinogens found in meat and charcuterie products. Sci Total Environ. 2015;514:33-41.
Huwe JK,et al. Polybrominated diphenyl ethers in U.S. Meat and poultry from two statistically designed surveys showing trends and levels from 2002 to 2008. Agric Food Chem. 2011 May 25;59(10):5428-34.
Key TJ,et al. Insulin-like growth factor 1 (IGF1), IGF binding protein 3 (IGFBP3), and breast cancer risk: pooled individual data analysis of 17 prospective studies. Lancet Oncol. 2010 Jun;11(6):530-42
Melnik BC, et al. The impact of cow’s milk-mediated mTORC1-signaling in the initiation and progression of prostate cancer. Nutr Metab (Lond) 2012 9(1):74.
Puangsombat K, et al.. Occurrence of heterocyclic amines in cooked meat products. Meat Sci. 2012;90(3):739-46.
Richman EL, et al. Choline intake and risk of lethal prostate cancer: incidence and survival. Am J Clin Nutr. 2012;96(4):855-63.
Rohrmann S, et al. Meat consumption and mortality–results from the European Prospective Investigation into Cancer and Nutrition. BMC Med. 2013;11:63.
Rowlands MA, et al. Circulating insulin-like growth factor peptides and prostate cancer risk: a systematic review and meta-analysis. Int J Cancer. 2009 May 15;124(10):2416-29.
Schecter A, et al. Polybrominated diphenyl ether (PBDE) levels in an expanded market basket survey of U.S. food and estimated PBDE dietary intake by age and sex. Environ Health Perspect. 2006 Oct;114(10):1515-20.
Sinha R, et al. Meat intake and mortality: a prospective study of over half a million people. Arch Intern Med. 2009;169(6):562-71.
Stewart BW, et al. World Cancer Report 2014. 2014.
Tse G, et al. Egg consumption and risk of GI neoplasms: dose-response meta-analysis and systematic review. Eur J Nutr. 2014;53(7):1581-90.
WCRF/AICR. World Cancer Research Fund / American Institute for Cancer Research. Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective.Washington DC: AICR, 2007
Zaidi R, et al. Rapid detection and quantification of dietary mutagens in food using mass spectrometry and ultra performance liquid chromatography. Food Chem. 2012;135(4):2897-903.
Zhang Y, et al. Mechanisms of breast cancer bone metastasis. Cancer Lett. 2010 Jun 1;292(1):1-7.
Want to know what I decided to eat after all of this research?
I can send you an email summary of what I decided and why!