red-meat-cancer

Processed Meat, Red Meat and Cancer

On the 24th October 2015, the World Health Organisation (WHO) released a report based on an evaluation by The International Agency for Research on Cancer (IARC), the cancer agency of WHO, on the ability of red meat and processed meat in the diet to cause cancer1.

The report lists red meat as probably carcinogenic and processed meat as carcinogenic, meaning that red meat is probably capable of causing cancer and processed meat consumption is capable of causing cancer. So what does it mean for us and why does consumption of these meats cause cancer?

What is processed meat?

processed meat
Most commercial sausages have undergone processing and preservation steps

Processed meat is meat that has been preserved in some way, either by natural smoking, salting or curing, or by the addition of artificial preservatives such as nitrites. Processed meat includes ham, bacon, salami, hotdogs and many commercial sausages.

The IARC has placed processed meat in the carcinogenic (cancer causing) category alongside substances such as alcohol, tobacco and asbestos. This means that the IARC has concluded that consumption of processed meat can cause cancer. The categorisation does not indicate risk level, so the IARC is not saying that processed meat consumption is just as likely as tobacco and asbestos to cause cancer, rather that in some cases it has the ability to do so.

Processed meat consumption has been strongly linked to colorectal cancer and it is estimated that up to 70% of these types of cancers are diet related2.

What is red meat?

red meat
Beef steak is an example of red meat

Red meat includes beef, pork, goat and lamb. Meat coming from these mammals contains the oxygen binding proteins, myoglobin and haemoglobin. It is primarily the myoglobin that gives the meat its red colour prior to cooking. Red meat has significant nutritional value, it contains iron, phosphorus, zinc, B-vitamins and lipoic acid. The IARC has classified unprocessed red meat as a probable carcinogen, meaning that its consumption is likely to be able to cause cancer, in some people.

The World Cancer Research Fund, the American Institute of Cancer Research3 and Cancer Research UK4 all acknowledge the link between red meat consumption and bowel cancer. It is thought that approximately 21% of bowel cancer cases in the UK are attributed to red meat consumption5.

How does eating red meat cause cancer?

The way in which non-processed red meat consumption can cause cancer is not fully understood. Possible theories include the high temperature cooking that red meat can be subjected to, and the high fat content of red meat, however scientific studies have done little to prove these theories. A more convincing risk factor seems to be related to the haem content of meat. Studies support the theory that when consumed, the haem content in red meat is broken down into N-nitroso compounds6 that damage the DNA lining of the gut and begin the cancerous process. The cells of the gut then proliferate more rapidly to try and counteract the irritation and this further exacerbates the problem.

Another interesting study suggests that unlike most mammals, humans do not have a unique sugar named Neu5Gc. Researchers from the University of California believe that this may explain why humans have a higher risk of cancer when they eat red meat, when no other animals exhibit the same risk. They believe that when humans eat red meat, in the absence of Neu5Gc, it triggers a chronic inflammatory immune response that may lead to tumour formation7.

Then add meat preservation steps into the mix

So if we consider that red meat consumption may cause cancer, let us examine what happens to the meat during commercial processing. In order to preserve the meat and prevent discolouration, artificial nitrites are often used. Nitrites enhance the pink colour of the raw meat, a quality that is perceived by the consumer as relating to the freshness of the product. These nitrites have been linked in scientific studies to cancer of the colon, rectum, liver, lung and pancreas8.

Smoking meat and high temperature cooking are additional preservation methods that might be used by the food industry. These methods cause polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs) to form and these are also considered to be carcinogenic9,10.

Scientists believe that eating a significant amount of red meat probably causes cancer. When this meat undergoes processing steps, the risk of cancer is further increased.

Conclusion

The WHO now recommends that you can take advantage of the nutritional benefits of fresh (unpreserved) red meat, but that you should eat no more than 500g of lean meat a week. There is no nutritional benefit to eating processed meat and this should be removed from your diet. Adding several meat-free meals a week to your diet will help to reduce your red meat consumption.

 

References:

  1. http://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(15)00444-1/abstract
  2. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2661797/
  3. http://www.wcrf.org/PDFs/Colorectal-cancer-report-summary-2011.pdf
  4. http://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/bowel-cancer/risk-factors#heading-Three
  5. http://www.ncbi.nlm.nih.gov/pubmed/22158315
  6. http://www.ncbi.nlm.nih.gov/pubmed?Db=pubmed&Cmd=ShowDetailView&TermToSearch=17956350&ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
  7. http://m.pnas.org/content/112/2/542.abstract
  8. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2121650/, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1913932/?tool=pubmed
  9. http://www.cancer.gov/about-cancer/causes-prevention/risk/diet/cooked-meats-fact-sheet
  10. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2661797/

 

About the author: 

Sonia Nicholas is a Biomedical Scientist and Freelance Clinical Science Writer & Editor. She has been working in the field of clinical science for fifteen years.

Sonia believes that everyone can improve their health by eating a clean diet – a claim that scientific research increasingly supports. Sonia also believes that healthy, clean eating is accessible to all and doesn’t have to be an expensive lifestyle choice.

All of the information on The Green Apple Club website is in line with current, recommended Government guidelines. All of the articles are evidence based and fully scientifically referenced.

 

Article tags: processed meat, red meat, cancer


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