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Health: Diet

Meat and cancer: Here is some perspective for doctors

Several leading Australian cancer authorities have jumped in to put perspective on the barbecue-stopping WHO report on the carcinogenic nature of red and processed meat.

The report, published in The Lancet Oncology, should not be a concern to Australians if they stick to the current National Health and Medical Research dietary guidelines, says the Cancer Council.

That is largely because the guidelines discourage processed meat.

The WHO group, led by Professor Bernard Stewart from UNSW and the Cancer Council, have classified the consumption of red meat as probably carcinogenic to humans (Group 2A). This association was observed mainly for colorectal cancer, but associations were also seen for pancreatic cancer and prostate cancer.

It classified processed meat as carcinogenic to humans (Group 1), based on sufficient evidence in humans that the consumption of processed meat causes colorectal cancer.

That is largely in sync with the Australian guidelines, which state that to reduce risk, Australians should eat 100 to 200g (raw weight) of red meat three to four times a week.

The guidelines have also moved processed meat out of the basic food groups to a list of discretionary foods which should be avoided by people who are overweight or inactive.

The International Agency for Research on Cancer, the cancer agency of the WHO, says processed meat, and probably all red meat, is carcinogenic to humans. This association was observed mainly for colorectal cancer, but is also relevant for pancreatic and prostate cancer.

According to the last ABS nutrition survey, women and children are more or less on the mark when it comes to their fresh red meat intake, eating slightly less than the recommended 450g of fresh red meat a week. But men are eating more than they should, averaging around 700g per week.

Dr Darren Saunders, a cancer researcher at UNSW, says the report must be put into perspective. "We are talking about less than 10 cases per thousand (difference) between high meat eating groups and low meat eating groups like vegetarians," he said on ABC radio.

"Something like 19% of all cancers are caused from smoking whereas something like 3% are caused by processed meat consumption."

The WHO report, which is based on the evidence from 1,000 studies, follows a Cancer Council research report that says more than 2600 bowel cancers diagnosed in Australia in 2010 could be attributable to processed and red meat consumption.

But people have little to fear if they follow the NHMRC dietary guidelines, says Kathy Chapman, chair of the Cancer Councilís Nutrition and Physical Activity Committee.

"We do not encourage avoiding red meat altogether. Lean red meat is a good source of iron, zinc, vitamin B12 and protein. Processed meats, however, are nutrient poor by comparison and more likely to be high in fat, salt and nitrates. This is why we are recommend reducing or limiting processed meat intake."

Q&A - What does it all mean?

Processed meat has been classified as carcinogenic to humans in the same way as tobacco and asbestos are.

What do I make of that?

This does not mean they are all equally dangerous. The International Agency for Research on Cancer classifications describe the strength of the scientific evidence about an agent being a cause of cancer, rather than assessing the level of risk.

Processed meat has been classified as Group 1, carcinogenic to humans.

What does this mean?

This category is used when there is sufficient evidence of carcinogenicity in humans. In other words, there is convincing evidence that the agent causes cancer. The evaluation is usually based on epidemiological studies showing the development of cancer in exposed humans. In the case of processed meat, this classification is based on sufficient evidence from epidemiological studies that eating processed meat causes colorectal cancer.

What types of cancers are we talking about?

The strongest, but still limited evidence for an association with eating red meat, is for colorectal cancer. There is also evidence of links with pancreatic cancer and prostate cancer. With processed meats, the IARC working group concluded that they cause colorectal cancer. An association was stomach cancer was also seen but the evidence is not conclusive.

Should patients still eat red meat?

Yes, lean red meat is a good source of iron, zinc, vitamin B12 and protein. But they should be advised not to eat no more than 100 to 200g (raw weight) a few times a week.

What about processed meats?

Processed meats are nutrient poor by comparison and more likely to be high in fat, salt and nitrates. People should try to reduce your intake of processed meats.

Do methods of cooking meat change the risk?

High-temperature cooking methods generate compounds that may contribute to carcinogenic risk, but their role is not yet fully understood so at this stage we canít recommend any particular cooking method.

Is eating raw meat safer?

From a carcinogenic point of view, we donít know but bear in mind the risk of infection from consumption of raw meat.

Red meat was classified as Group 2A, probably carcinogenic to humans.

What does that mean exactly?

In the case of red meat, the classification is based on limited evidence from epidemiological studies showing positive associations between eating red meat and developing colorectal cancer as well as strong mechanistic evidence. Limited evidence means that a positive association has been observed between exposure to the agent and cancer but that other explanations for the observations (technically termed chance, bias or confounding) could not be ruled out.

Why does meat cause cancer?

It is not fully understood how cancer risk is increased by red meat or processed meat.

Contributed by Amanda Davey: Medical Observer - medical news, opinion and analysis

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