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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.

GentlePurpleRain
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TheJulyPlot
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    This article seems to better correspond to the OP claim: http://www.nzherald.co.nz/lifestyle/news/article.cfm?c_id=6&objectid=11534891 – DavePhD Jun 05 '17 at 13:43

2 Answers2

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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.

DavePhD
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  • Does this equate to 500 grams of processed meat a day increasing the risk of colorectal cancer by a factor 10.1 - 10.3? – TheJulyPlot May 31 '17 at 16:42
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    Since the cited study is "red and processed meat," and the original claim intentionally conflates the two, despite the actual studies pointing at processed meats, what did that study have to say about red, non-processed meat? Can't view the link right now because of firewall. The substance of concern, if I recall correctly, are the nitrites, correct? – PoloHoleSet May 31 '17 at 16:47
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    @TheJulyPlot No, it is non-linear and plateaus around 140 grams/day. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3108955/ – DavePhD May 31 '17 at 16:49
  • What about the smokers, how does the amount they smoke impact their chances of getting cancer. The 15 to 30 times number has quite a large variance. – TheJulyPlot May 31 '17 at 16:52
  • @TheJulyPlot you can used this tool http://nomograms.mskcc.org/Lung/Screening.aspx to analyze your particular circumstances. – DavePhD May 31 '17 at 16:58
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    That 50 grams per day is day in, day out, over a long course of time. That's the equivalent of eating three quarters of a pound of bacon every week. – David Hammen May 31 '17 at 17:01
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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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    @PoloHoleSet apparently 1-2 pounds of bacon in a whole year is typical in the US https://www.statista.com/statistics/282269/us-households-amounts-of-bacon-consumed-trend/ – DavePhD May 31 '17 at 17:15
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    This is very good information Dave, but this doesn't really answer the question as the measurements do not equate to each other in terms of risk increases for a given amount of processed meat per day vs a given amount of cigarettes per day. I understand that exact numbers are hard to come by due to variances in circumstances. But there is still no clear answer to say the World Health Organisation are wrong to say that processed meat ranks alongside cigarettes as a major cause of cancer. – TheJulyPlot May 31 '17 at 17:21
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    @TheJulyPlot It obviously can't compare to cigarrettes. Those numbers are _extreme_ - Most people don't eat only processed red meat, but other non-processed alternatives too - like steak or poultry. This answer is very good. – T. Sar May 31 '17 at 17:28
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    @TheJulyPlot In other words - part of being skeptic is accepting an answer even if it's exactly what you wanted. – T. Sar May 31 '17 at 17:28
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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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    I had a comment in the question about how the original claim conflated processed meat with red meat, and claimed that the broad category (known source of cancer) = "just as bad a cigarettes," but our ever-zealous moderators nuked it, despite it's specific relevance to the topic and the claim. Same as it ever was..... – PoloHoleSet May 31 '17 at 19:18
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    Relative risk shouldn't be used, but absolute risk. Doubling my chance of dying in a car crash is more concerning than tripling my chance of being killed by a falling tree branch. – Andrew Grimm May 31 '17 at 22:52
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    @AndrewGrimm I agree, that's why I have the part about deaths from lung cancer being more than from colorectal cancer. – DavePhD May 31 '17 at 23:49
  • So you did. Sorry. – Andrew Grimm Jun 01 '17 at 00:35
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    @DavidHammen Not to mention that stomach cancer was a major cancer back before refrigeration and modern preservation techniques, and is nearly non-existent now. Food that contains moulds, bacteria and their products etc. is a cancer risk - but "cultured" moulds and bacteria are a lot less dangerous than the ones running in the wild. That's why humans started making things like ham and cheese long before we understood how exactly it prevents food from spoiling (which is basically by spoiling it in a controlled, safe manner). Raw meat needs a lot more precautions and freshness than cured meat. – Luaan Jun 01 '17 at 07:58
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    Looking at cancer research UK’s analysis, this suggests that 3% of all cancers in the UK are due to processed meat, with 19% being down to smoking. The % of smokers is considerably lower than red and processed meat eaters, although smokers tend to consume a lot more of the carcinogenic substance then red and processed meat eaters. So while processed meat is in the same group as smoking as being a cause of cancer the risk is a lot lower. Although the risk associated with processed meat does seem to be significant. I am going to mark this answer as correct. – TheJulyPlot Jun 01 '17 at 09:01
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    "In 2011, scientists estimated that around 3 in every hundred cancers in the UK were due to eating too much red and processed meat (that’s around 8,800 cases every year). This compares against 64,500 cases every year caused by smoking (or 19 per cent of all cancers)." http://scienceblog.cancerresearchuk.org/2015/10/26/processed-meat-and-cancer-what-you-need-to-know/?_ga=2.263068361.497663973.1496306835-1724676155.1496306835 – TheJulyPlot Jun 01 '17 at 09:01
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    The last paragraph is misleading. Correlation does not imply causality. You are implying that all the lung cancer are caused by smoking, and all colorrectal cancer is caused by red meat and the amount of smokers and red meat eaters is not taken into account in those figures. – Mindwin Remember Monica Jun 01 '17 at 13:52
  • @Mindwin To me the last paragraph just reads as an 'FYI this is supported by the fact that the type of cancer most associated with smoking is way less likely to kill you than the type of cancer most associated with eating red/processed meat' – Brent Hackers Jun 01 '17 at 14:02
  • @Mindwin That's not what I'm saying at all. Instead, since in the earlier part of the answer I only give relative risk compare to two different things (baseline lung cancer and baseline colorectal cancer), in the last sentence I am linking to absolute numbers so that the reader will understand that the much more severe increase in risk due to smoking is not negated by a much lesser risk of getting lung cancer in the first place. – DavePhD Jun 01 '17 at 14:05
  • in skeptics, if you are throwing a number in your answer, you have to show the relevance of that number, otherwise it is just noise. You just showed that more people die from lung than colorectal cancer. But also more people die from car accidents than monocycle accidents, and this does not mean monocycles are safer. maybe less people ride monocycles and the death rates normalized by 1000 users is the same. You fail to show that correlation. – Mindwin Remember Monica Jun 01 '17 at 15:41
  • @Mindwin In US, 50,260 died of colorectal cancer in a year. Worst case scenario would be if that represented zero processed meat eaters, and suddenly everyone started eating maximal processed meat. Then according to Fig. 3 of the 2011 reference 1.33(50,260) people would die of colorectal cancer. 16,585 deaths is the maximum possible colorectal cancer deaths due to processed meat. Yet 155,870 died of lung cancer in the year, most of which are due to smoking http://www.lung.org/lung-health-and-diseases/lung-disease-lookup/lung-cancer/resource-library/lung-cancer-fact-sheet.html – DavePhD Jun 01 '17 at 15:57
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    @PoloHoleSet [Relevant XKCD](https://xkcd.com/418/) – Michael Jun 01 '17 at 19:11
  • Cheers, perfect :) – Lightness Races in Orbit Jun 02 '17 at 13:36
  • Not to be pedantic, but shouldn't that say "increase the risk ... by a factor of 0.1 - 0.3"? – Matt Malone Jun 02 '17 at 16:10
  • @MattMalone to me "factor of" means multiplication. – DavePhD Jun 02 '17 at 16:28
  • Yes. It's the combination of multiplication ("factor") and addition ("increase") that makes it seem incorrect to me. 100 increased by a factor of 0.25 (25%) is 125. 100 increased by a factor 1.25 (125%), then, would be 225. 100 scaled (not increased) by a factor of 0.25 is 25. 100 scaled by a factor of 1.25 is 125. – Matt Malone Jun 02 '17 at 18:52
  • @Matt Malone https://ell.stackexchange.com/questions/52706/what-does-reduce-by-a-factor-of-10-mean-in-terms-of-percentage-in-the-followin – DavePhD Jun 02 '17 at 20:29
  • What are the base rates of these different kinds of cancers without these risk factors? – rakslice Jun 02 '17 at 22:54
  • @rakslice "The age-standardized lung cancer death rates among never-smoking men and women in CPS-II were 17.1 and 14.7 per 100 000 person-years" https://pdfs.semanticscholar.org/9519/7bdfaef35d0d75970a436f1f0f43a779c768.pdf – DavePhD Jun 03 '17 at 02:00
  • @rakslice for colorectal cancer, the death rate is 14.8 per 100,000 according to https://seer.cancer.gov/statfacts/html/colorect.html. I don't have a direct statistic for without the risk factor. I guess that would be the rate for lifelong vegetarians. Basically the death rate for colorectal cancer including people with risk factors is about the same as the lung cancer death rate for non-smokers. – DavePhD Jun 03 '17 at 12:46
  • @rakslice see also " out of every 1000 people in the UK, about 61 will develop bowel cancer at some point in their lives. Those who eat the lowest amount of processed meat are likely to have a lower lifetime risk than the rest of the population (about 56 cases per 1000 low meat-eaters)." http://scienceblog.cancerresearchuk.org/2015/10/26/processed-meat-and-cancer-what-you-need-to-know/ – DavePhD Jun 05 '17 at 13:47
  • @DavePhD A cigarette has closer to 2 full grams of tobacco in it. Not 0.7. I've split them open and weighed the innards on a coke scale multiple times. – WakeDemons3 Jun 08 '17 at 21:26
  • @WakeDemons3 next question: is cocaine as bad for your health as smoking? – Andrew Grimm Mar 06 '18 at 11:10
  • @AndrewGrimm Nope. Smoking (tobacco) is worse. – WakeDemons3 Mar 06 '18 at 15:11
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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.

David Hammen
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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 01 '17 at 11:22
  • The source https://www.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 01 '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 01 '17 at 16:36
  • So "in the same category" is technically true, but has often been misinterpreted. – aschepler Jun 05 '17 at 00:22
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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 05 '17 at 19:58