Tuesday October 27 2015

Processed meats have been linked to bowel cancer

What is the issue?

“Processed meat ranks alongside smoking as major cause of cancer, World Health Organisation [WHO] says,” The Daily Telegraph reports. It has been ranked as a group one carcinogen – the same ranking as cigarettes, alcohol and asbestos.

The WHO’s International Agency for Research on Cancer (IARC) released a report evaluating the link between the consumption of red and processed meat and cancer. A question and answer factsheet was also published.

The report explained red meat refers to unprocessed meat such as beef, veal, pork and lamb, while processed meat has been transformed through salting, curing, fermentation, smoking, or other processes.

The largest body of evidence is for the link with colorectal (bowel) cancer. 

How was the report received by the media?

The quality of the UK media’s reporting was mixed. Some sources fell into the trap of assuming that since processed meat had been ranked as a group one carcinogen, it meant it was as dangerous as other substances in the group. This led to headlines such as the Daily Express’, “Processed meat is as bad as smoking”, which is simply untrue.

While any substance ranked as a group one carcinogen is known to cause cancer, this doesn’t meant the risk of cancer is the same for all substances. A bacon sandwich is not as dangerous as being exposed to weapons grade plutonium, and smoking a pack of 20 cigarettes a day is far deadlier than eating a ham roll.

The Daily Mail and The Guardian did make an effort to put the risk of eating processed meat into context. Both papers, via their respective websites, provided a link to an extremely useful infographic produced by Cancer Research UK.

A key statistic provided by the infographic is that if everyone stopped smoking, there would be 64,500 fewer cases of cancer a year in the UK, compared with 8,800 fewer cases if everyone stopped eating processed or red meat.  

What evidence is the advice based on?

The link between red and processed meat and cancer is not new, and there has been a large body of research evidence to suggest bowel cancer is more common when these food items are consumed. According to Cancer Research UK, 21% of bowel cancers and 3% of all cancers are caused by red meat.

The WHO Working Group assessed more than 800 observational studies that investigated the association between cancer and the consumption of red meat across a range of countries, ethnicities and diets.

Data from the studies was analysed to investigate the link. Studies that were better quality, where the observations were prospective – that is, diet was assessed before looking at cancer development – were considered more reliable, and their findings were given greater weight.

The researchers also preferentially looked for studies with larger sample sizes, that had used validated questionnaires, and had controlled for potential health and lifestyle confounders that may be influencing the link. However, it was not possible to avoid all sources of bias and confounding, particularly for red meat, where data availability was limited.  

What are the risks?

Positive links between colorectal cancer and processed meat were found in 12 of 18 cohort studies and six of nine case-control studiesexamining the meat.

Looking at a review that had pooled the results of 10 cohort studies, the Working Group found an increase of 100g of red meat a day increased the risk of colorectal cancer by 17% (95% confidence interval [CI] 1.05 to 1.31), and 50g of processed meat a day increased the risk by 18% (95% CI 1.10 to 1.28).

There was also data available linking red meat consumption withpancreatic cancer and prostate cancer, and processed meat withstomach cancer.

As a result of these findings, the WHO Working Group has classified processed meat as “carcinogenic to humans” on the basis of sufficient evidence to draw a link with colorectal cancer and an association with stomach cancer.

There was a limited amount of evidence available when assessing red meat, and this was therefore classified as “probably carcinogenic to humans”. 

How much red meat is it safe to eat?

The advice from the WHO Working Group supports current public health recommendations to limit intake of red and processed meat.

If you currently eat more than 90g (cooked weight) of red and processed meat a day, the Department of Health advises you cut down to 70g.

Ninety grams is equivalent to around three thinly cut slices of beef, lamb or pork, where each slice is about the size of half a piece of sliced bread. A cooked breakfast containing two typical British sausages and two rashers of bacon is equivalent to 130g.

It is unnecessary to cut red meat out all together as it is a good source of nutrients, including protein, iron, zinc and vitamin B12.

If you currently eat a large amount of red and processed meats, it might be good for you to cut down. Some ways to do this are:

• eating smaller portions of meat
• switching to chicken or fish
• keeping a few days a week red meat-free
• add beans or pulses such as kidney beans, chickpeas and lentils to replace some of the meat in dishes
• instead of bacon, chorizo or salami, use chicken or vegetarian sausages

Analysis by Bazian. Edited by NHS Choices. Follow NHS Choices on Twitter. Join the Healthy Evidence forum.