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I recently saw this posted on social media; it caused quite a stir, with over 200 comments from people debating the veracity of the claims.

“It’s funny how people get outraged at parents putting their kids at risk by defying scientific fact and basic logic by not getting them vaccinated. Yet they still feed their kids red and processed meat, despite the fact that it is proven to cause as much cancer as smoking (plus a load of other health and environmental problems).

It’s amazing how people are so easily manipulated into making poor decisions based on social norms.

It’s also amazing that people find the idea of banning the consumption of red meat cadavers to under 18s wacky and mad. Ahh humans…how can we have come so far yet still be capable of being so illogical.

(Also if your first reaction to this is “bacon” you’re as unimaginative as you are daft.)”

It was later clarified that “despite the fact that it is proven to cause as much cancer as smoking” was meant in relative terms. i.e. One processed hamburger raises the risk of cancer roughly as much a 3 cigarettes. (This was given as an example rather than an actual equivalent measurement.)

Basically, the claim was that in equivalent terms, meat causes as much cancer as smoking. (i.e. Not the total cases of cancer as people get more carcinogens from smoking because they smoke a higher number of cigarettes.)

Dose the claim “processed meat causes as much cancer as smoking in relative terms” hold up to scrutiny?


Edit:
The basis of this claim appears to be from claims made by the World Health organisation. As stated in this guardian article:

Bacon, ham and sausages rank alongside cigarettes as a major cause of cancer, the World Health Organisation has said, placing cured and processed meats in the same category as asbestos, alcohol, arsenic and tobacco.

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According to the US CDC:

People who smoke cigarettes are 15 to 30 times more likely to get lung cancer or die from lung cancer than people who do not smoke

According to Carcinogenicity of consumption of red and processed meat (Lancet 2015) citing to Red and Processed Meat and Colorectal Cancer Incidence: Meta-Analysis of Prospective Studies (2011):

Positive associations of colorectal cancer with consumption of processed meat were reported in 12 of the 18 cohort studies...an 18% increase (95% CI 1·10–1·28) per 50 g per day of processed meat

In other words, smoking will increase risk of lung cancer by a factor of 15-30, while 50 grams a day of processed meat will increase the risk of colorectal cancer by a factor 1.1-1.3.

Furthermore, it is found that at high levels of processed meat consumption, the risk levels off, never exceeding 1.4 relative risk (see Fig. 3 of 2011 reference).

Additionally, the annual number of US deaths from lung cancer (155,870) is greater than from colorectal cancer (50,260). See https://www.cancer.gov/types/common-cancers.

Taken together, the <1.4 maximum relative risk factor and the 50,260 annual colorectal cancer deaths, there is an upper limit (supposing everyone switched from zero processed or red meat to maximal processed meat) of 20,000 deaths due to the processed meat consumption, whereas most of the 155,870 lung cancer deaths are due to smoking.

So, "no", eating processed meat is not as bad as smoking a typical amount that a smoker smokes.

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    @DavidHammen - "That's the equivalent of eating three quarters of a pound of bacon every week." - aka "living the dream." – PoloHoleSet May 31 '17 at 17:11
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    @TheJulyPlot What would you compare? Grams of smoke versus grams of processed meat? Grams of tobacco versus grams of processed meat? A cigarette has about 0.7 grams of tobacco. It makes more sense to compare a typical smoker's excess risk to a typical processed-meat user's excess risk. – DavePhD May 31 '17 at 17:34
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    @TheJulyPlot The fact that the process meat risk plateaus above 140 grams per day, with relative risk being less than 1.4 completely proves that cigarette smoking is worse by at least a factor of 10. – DavePhD May 31 '17 at 17:40
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    @TheJulyPlot -- The WHO do not claim that processed meat is a major cause of cancer. They instead claim that processed meat is a known cause of cancer. Big difference. – David Hammen May 31 '17 at 18:19
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    @DavidHammen Yes, you're correct. It was the Guardian article that incorrectly used the word 'major,' not the WHO. The Guardian's claim about WHO "placing it in the same category as asbestos, alcohol, arsenic, and tabacco" is technically true, but incredibly misleading without context. WHO places everything that has a known causal link, regardless of how large or small the risk increase, in that same category. – reirab May 31 '17 at 19:00
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Does the claim “processed meat causes as much cancer as smoking in relative terms” hold up to scrutiny?


No, it does not. The WHO did indeed classify processed meat as carcinogenic to humans. Going to the source, http://www.who.int/features/qa/cancer-red-meat/en/,

9. Processed meat was classified as carcinogenic to humans (Group 1). Tobacco smoking and asbestos are also both classified as carcinogenic to humans (Group 1). Does it mean that consumption of processed meat is as carcinogenic as tobacco smoking and asbestos?

No, processed meat has been classified in the same category as causes of cancer such as tobacco smoking and asbestos (IARC Group 1, carcinogenic to humans), but this does NOT mean that they are all equally dangerous. The IARC classifications describe the strength of the scientific evidence about an agent being a cause of cancer, rather than assessing the level of risk.

In other words, just because both tobacco cigarettes are and eating processed meat are known to cause cancer does not mean they are equally bad for you.

So how bad is eating processed meat? Once again going to the source of that pronouncement,

12. How many cancer cases every year can be attributed to consumption of processed meat and red meat?

According to the most recent estimates by the Global Burden of Disease Project, an independent academic research organization, about 34 000 cancer deaths per year worldwide are attributable to diets high in processed meat.

Eating red meat has not yet been established as a cause of cancer. However, if the reported associations were proven to be causal, the Global Burden of Disease Project has estimated that diets high in red meat could be responsible for 50 000 cancer deaths per year worldwide.

These numbers contrast with about 1 million cancer deaths per year globally due to tobacco smoking, 600 000 per year due to alcohol consumption, and more than 200 000 per year due to air pollution.

13. Could you quantify the risk of eating red meat and processed meat?

The consumption of processed meat was associated with small increases in the risk of cancer in the studies reviewed. In those studies, the risk generally increased with the amount of meat consumed. An analysis of data from 10 studies estimated that every 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by about 18%.

The cancer risk related to the consumption of red meat is more difficult to estimate because the evidence that red meat causes cancer is not as strong. However, if the association of red meat and colorectal cancer were proven to be causal, data from the same studies suggest that the risk of colorectal cancer could increase by 17% for every 100 gram portion of red meat eaten daily.

This does not mean that a single 50 gram of processed meat increases your chance of colorectal cancer by 18%. That 50 grams is the average amount consumed per day over the course of years. That's three quarters of a pound of bacon every week of the year. That represents a significant risk of obesity as well as a slight increase in the risk of colorectal cancer.

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    +1 - this is most likely what lead to the quoted poster's confusion. I recall there being a lot of confusion at the time the WHO reclassified processed meats. – JBentley Jun 1 '17 at 11:22
  • The source ncbi.nlm.nih.gov/pmc/articles/PMC3045642 bizarrely excludes bacon from processed meats saying "Processed meat, by MPED definition (29), included frankfurters, sausage, and luncheon meats (made from meat or poultry), but did not include cured meats, such as ham or bacon". – DavePhD Jun 1 '17 at 14:28
  • @DavePhD -- I was using bacon as canonical. So use 3/4 lb per week of kielbasa instead of bacon. That's still a lot. – David Hammen Jun 1 '17 at 16:36
  • So "in the same category" is technically true, but has often been misinterpreted. – aschepler Jun 5 '17 at 0:22
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    @DavePhD Yeah, it's strange that they seem to have chosen a definition of "processed" that focuses on grinding stuff up and changing its shape, rather than on the actual composition of the food. Maybe they couldn't bring themselves to admit that bacon is bad for them. – David Richerby Jun 5 '17 at 19:58

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