Pig meat and cancer

Australian readers may be familiar with “Sunrise“, the high-rating breakfast program on the Seven Network. It is sponsored by Australian Pork Limited (APL) (the national peak industry body), and features advertisements encouraging viewers to “get some pork on your fork“. [1, 2]

Paradoxically, Sunrise also features many stories on the subject of cancer.

Why is this a paradox?

The reason is that pig meat has been identified as a key factor in colorectal (bowel) cancer risk. To my knowledge, none of Sunrise’s segments on cancer have mentioned pig meat, but any relating to colorectal cancer should have.

World Cancer Research Fund International (WCRF International) published its Second Expert Report in 2007, titled “Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective”. The report was issued jointly with one of WCRF’s network members, the American Institute for Cancer Research. [3]

WCRF International is a not-for-profit umbrella association that leads a global network of cancer charities funding research and education programmes into the link between food, nutrition, physical activity, weight maintenance and cancer risk.

The report contained recommendations relating to red and processed meat (Recommendation 5, Chapter 12).

Pig meat considered to be red and processed meat for the purpose of the analysis

For the purpose of the analysis, beef, pork, lamb, and goat were all considered to be forms of red meat.

Processed meat consisted of meat preserved by smoking, curing or salting, or addition of chemical preservatives. Such meat includes ham and bacon.

How much can you eat safely?

So how much red or processed meat does WCRF International suggest you can eat safely?

Red Meat: No more than 500 g (cooked weight) per week.

Processed meat: Very little, if any.

WCRF International has stated:

“The evidence that red meat is a cause of colorectal cancer is convincing. The evidence that processed meat is a cause of colorectal cancer is also convincing.” (page 382)

WCRF UK has stated: “The Panel of Experts could find no amount of processed meat that can be confidently shown not to increase cancer risk. That is why WCRF UK recommends people avoid processed meat to reduce their bowel cancer risk. ” [4]

Update

As part of WCRF International’s Continuous Update Project, in 2010, a research team at Imperial College London produced an updated systematic literature review of the evidence from 263 new papers on food, nutrition and physical activity. [5]

WCRF International’s Expert Panel considered the updated evidence and agreed that the findings confirmed or strengthened the convincing and probable conclusions of the Second Expert Report for colorectal cancer.

The problem with red and processed meat (including ham and bacon)

WCRF has reported that several hypotheses have been tested that may explain why consuming processed meat increases bowel cancer risk. Here are the main ones, all of which also appear to be relevant to red meat generally. [4]

Firstly, nitrites and N-nitroso compounds (NOCs):
Nitrites are preservatives that can react with certain compounds in protein-rich foods to produce NOCs, particularly in the absence of inhibitors such as vitamin C and in the presence of enhancers such as red meat. Many NOCs are carcinogenic. They can be formed during the curing process, and are also formed in the body from ingested nitrites and nitrates in red and processed meat.

Secondly, haem in red meat:
Haem is an iron-containing molecule present in animal blood and meat, especially red meat. Free iron can induce the production of free radicals, which can damage cell DNA. Haem can also induce the formation of NOCs in the body.

Finally, high-temperature cooking:
Cooking meat at a high temperature, especially frying and grilling, can cause the formation of certain carcinogenic compounds.

Some good news: plant foods help

The report also recommended that we eat mostly foods of plant origin to protect against a range of cancers.

Specifically: (a) Eat at least five servings (at least 400 g) of a variety of non-starchy vegetables and of fruits every day; (b) Eat relatively unprocessed cereals (grains) and/or pulses (legumes) with every meal; (c) Limit refined starchy foods; (d) People who consume starchy roots or tubers as staples should also ensure intake of sufficient non-starchy vegetables, fruits, and pulses (legumes).

While it reported, “foods containing dietary fibre probably protect against cancers of the colorectum”, it has since reported that the evidence has been upgraded from “probable” to “convincing”. [5]

It also reported that garlic probably protects against cancers  of the colon and rectum.

Other recommendations:

Here is the full list of recommendations in summary form: (a) Be as lean as possible within the normal range of body weight; (b) Be physically active as part of everyday life; (c) Limit consumption of energy-dense foods and avoid sugary drinks; (d) Eat mostly foods of plant origin; (e) Limit intake of red meat and avoid processed meat; (f) Limit alcoholic drinks; (g) Limit consumption of salt and avoid mouldy cereals (grains) or pulses (legumes); (h) Aim to meet nutritional needs through diet alone, without supplements; (i) Mothers to breastfeed; children to be breastfed; (j) Cancer survivors to follow the recommendations for cancer prevention.

Conclusion

Many media reports on cancer focus on the supposed need to raise funds for cancer research. Even if we disregard the potential inefficacy of much research, wouldn’t we achieve more by educating people on preventative measures?

Also, shouldn’t advertisements for red and processed meat (including pig meat) be banned or contain a health warning? If that’s considered necessary for tobacco products, then why not also for relevant meat products?

Footnote: None of the material contained in this article should be construed as representing medical, health, nutritional, dietary or similar advice.

Author: Paul Mahony (also on Slideshare,  Scribd, and Twitter)

References:

[1] Australian Pork Limited, http://australianpork.com.au/about-us/australian-pork-limited/

[2] Australian Pork Limited, Industry Focus, “Get some pork on your fork”, http://australianpork.com.au/campaigns/get-some-pork-on-your-fork/

[3] 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, http://www.dietandcancerreport.org/expert_report/report_contents/index.php and http://www.dietandcancerreport.org/cancer_resource_center/downloads/Second_Expert_Report_full.pdf, Chapter 12

[4] World Cancer Research Fund UK, “Informed – Issue 36, Winter 2009”, http://www.wcrf-uk.org/cancer_prevention/health_professionals/informed_articles/processed_meat.php

[5] World Cancer Research Fund International, Colorectal Cancer, Latest Evidence, http://www.dietandcancerreport.org/cup/current_progress/colorectal_cancer.php

Image: Aussie Farms (aussiefarms.org.au and aussiepigs.com). Reported to be from Landsdowne Piggery, New South Wales, Australia

Further reading: More information on the work of WCRF International can be found in “CSIRO Perfidy” by Geoff Russell, Vivid Publishing, 2009, http://www.perfidy.com.au/

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