Last month, over twenty leading scientists from across the globe met at the International Agency for Research on Cancer (IARC) in France to review the evidence and determine the effects of red meat consumption and processed meat consumption on cancer risk.
The experts assessed over 800 studies that looked at the relationship between over a dozen different cancers and the consumption of processed and red meat. The research studies spanned many different countries and populations, and included diverse diets. The bulk of evidence came from large quality studies carried out over the past two decades.
Processed meats like sausages and bacon can be treated in different ways; salting, fermentation, smoking and curing. These processes (particularly smoking and curing) can introduce carcinogenic substances to the meat; N-nitroso-compounds and polycyclic aromatic hydrocarbons. Cooking at high temperatures can also produce carcinogens such as heterocyclic aromatic amines and polycyclic aromatic hydrocarbons.
The International Agency for Research on Cancer (IARC) is the cancer agency of the World Health Organisation (WHO). In a startling new report, IARC have classified processed meat as “carcinogenic to humans” because of strong evidence linking consumption to the development of colorectal cancer. There was also an association between processed meat consumption and stomach cancer risk.
Researchers estimated that every 50g portion of processed meat consumed daily would increase the risk of developing colorectal cancer by 18 percent! Though the risk at the individual level is small, it increases with the quantity of processed meat consumed. From a public health perspective the study findings could not be more important. In light of the large and ever increasing number of people who routinely consume processed meat, the findings have strong implications for global cancer incidence if taken into account by individuals, governments and health care practitioners.
Steak over sausage?—What about unprocessed red meat?
This recent review of available global data has led the World Health Organisation to classify red meat consumption as “probably carcinogenic to humans”.
The IARC category of “probably carcinogenic to humans” also lists the chemotherapy agents cisplatin and etoposide, and the antibiotic chloramphenicol. More surprisingly, also listed in this category are shift work (that disrupts sleeping patterns), working as a hairdresser/barber (due to occupational exposures), and emissions from high temperature frying (aka cooking oil fumes).
The decision to classify red meat as “probably carcinogenic to humans” was based on a review of all the relevant data which highlighted strong mechanistic evidence for a carcinogenic effect related to consumption. The increased cancer risk was mainly observed for colorectal cancer, but also pancreatic and prostate cancer. Although more difficult to estimate the increased risk posed by red meat consumption compared to processed meat consumption due to confounding factors, IARC postulated that if a causal relationship were to be categorically proven, then for every 100g portion of red meat eaten daily, the risk for colorectal cancer could increase by 17%.
Interestingly, high red meat consumption in pre-menopausal women has also been associated with a higher risk for developing breast cancer.
Global trends—How much meat do we eat?
Global meat consumption varies greatly depending on country. In some countries meat is eaten by less than 5% whereas in others it is close to 100%. Processed meat consumption varies also, from less than 2% to about 65%. Most people who consume red meat eat about 50-100g per day. According to the study, high consumption was classified as greater than 200g per person per day.
- In a 2011 report, The American Institute for Cancer Research (AICR) estimated that approximately 45% of colorectal cancer cases could be prevented if people consumed more fiber-rich plant foods, consumed less meat and alcohol, became more physically active, and maintained a healthy weight.
- The World Cancer Research Fund/AICR Continuous Update Project, indicated that there was convincing evidence linking diets high in red and processed meat to increased colorectal risk
- The American Cancer Society’s Cancer Prevention Study II has specifically recommended limiting consumption of red and processed meat since 2002.
Corporate interests: Unsurprisingly, the IARC WHO report findings were not welcomed by the meat industry which criticised the findings as lacking common sense and being “unscientific”.
Take home messages: Eliminate processed meats best you can, and limit red meat consumption. Eat organic, ethically grown meat to reduce your environmental footprint, and to enjoy the benefits of meat not pumped full of antibiotics, hormones, and GMO crop feed. A recent study analysing meat samples found 15% contained strains of antibiotic resistant bacteria. It is often said that one third of the crops grown on Earth are used to feed animals. Scandalous in an age where people still starve to death.
Bouvard, V. Loomis, D. Guyton, K. (2015) Carcinogenicity of consumption of red and processed meat. Lancet Oncol. Published online ahead of print: October 26, 2015