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I just read an article in the german magazine "Der Spiegel" about a recent study claiming that 40% of all cancers are preventable. The article states specifically that one of the factors is the consumption of red meat:

Der Mangel an Früchten und Gemüse sowie der übermäßige Verzehr von Fleisch und Salz sollen für mehr als neun Prozent aller Krebsfälle verantwortlich sein.

Translated to english this passage reads as

The lack of fruit and vegetables as well as the excessive consumption of meat and salt are claimed to be responsible for more than nine percent of cancer cases

I knew that meat consumption is said to contribute to some health conditions, but I haven't heard about the association with cancer yet.

Is there solid scientific evidence to link the consumption of meat with a higher risk for developing cancer?

George Chalhoub
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Mad Scientist
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    As with all questions like this it isn't enough to know whether there is any relationship, it is important to know whether the relationship is *significant*. Also whether there is a component of trading one risk for another (slightly simplistic example, people who eat meat are less likely to be anaemic than those who don't: the question is which is a bigger and more serious effect?) – matt_black Dec 09 '11 at 14:10
  • I’m especially doubtful about their mention of salt and lack of vitamins. Vitamin deficiency is extremely rare in Western societies, almost all vitamin additives are pure pseudoscience (I thought we had a question about this, can’t find it now, but Spiegel covered this recently). And concerning salt, [the jury is still very much out](http://skeptics.stackexchange.com/q/415/82). – Konrad Rudolph Mar 30 '12 at 14:22
  • The question is tautological, because `exceeding consumtion` is by definition `exceeding`. Exceeding consumption of table water is exceeding as well. – user unknown May 08 '12 at 17:07

3 Answers3

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The article in Der Spiegel (and this very similar article on the BBC website) are based on this study in the British Journal of Cancer - The fraction of cancer attributable to lifestyle and environmental factors in the UK in 2010

According to the study eating meat is a risk factor, although other factors (e.g. smoking) are more significant.

Number and percentage of cancer cases in the UK attributable to different exposures.

Tom77
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    In addition, the "eating meat" is too broad. It may be due to consuming carcinogens resulting from specific meat preparation methods - please clarify whether the study makes the distinction. From looking at their tables, they: 1. have "Red and preserved meat", not all meat; and 2. don't specify whether preservation - or other factors - were what contributed. All in all, it may be good science but extremely poor argument against meat-eating. – user5341 Dec 08 '11 at 15:21
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    According to the image, fruit and vegetables seem to be the bigger problem. Maybe eating nothing is the best method to avoid cancer - just die from hunger! ;) – user unknown Dec 09 '11 at 02:43
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    @userunknown - if you read TFA, the fruity bar is from NOT eating ENOUGH of fruits and vegetables, not from eating them – user5341 Dec 09 '11 at 05:28
  • @DVK Good point! It is quite well known that salted and pickled foods contribute to cancer risk (mostly throat and mouth) because the preservation is imperfect, thus small pockets are able to putrefy and produce carcinogenic chemicals. – Superbest Mar 30 '12 at 16:42
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    @Superbest: I don't have citations, but there simply have to be huge health problems caused by factory farmed meat that's full of synthetic hormones, fed grain instead of grass, treated inhumanely, and then heavily processed with carcinogenic preservatives (nitrates, smoke, etc.). This, of course, is the meat that almost everyone eats. – Joshua Frank May 09 '12 at 01:45
  • @JoshuaFrank Not really. Brazil's meat has some rigorous quality control that mostly use genetic selection to raise cattle. Hormonal treatments and carcinogenic pesticides are forbidden by law. What other places call "Organic Meat" is just regular meat for us. This is also true on a lot of other countries, too! – T. Sar May 11 '15 at 12:24
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    I would take this chart with a grain of salt.... it has `Radiation - ionising` and `Radiation - UV`, this separation would imply that `Radiation - UV` is NON ionising UV radiation which is pretty much 'normal' light... (ionising means to have enough energy to 'kick' out molecules from cells and with out kicked out molecules there will be no mutations. No mutations - no cancer... If however `Radiation - UV` is ionising then why is it separated from `Radiation - ionising`? Something does not add up.... or maybe I am missing something here.... – Matas Vaitkevicius Dec 20 '16 at 16:26
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    @MatasVaitkevicius Maybe they separated out UV because it's a more common band to be exposed to while sunbathing etc? – endolith Jun 08 '17 at 15:52
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To briefly answer your question: meat consumption is correlated with some cancers.

Medical studies involving statistics look at correlation, not causation.

In the answer to the question Is a vegetarian (vegan) diet more healthy?, I cited an epidemiological study that may be found in Am J Clin Nutr September 1988 vol. 48 no. 3 739-748 (which you may read in full. It compares a large number (n=27,529) of Seventh-Day Adventists.

The conclusion is:

Within this population, meat consumption was positively associated with mortality because of all causes of death combined (in males), coronary heart disease (in males and females), and diabetes (in males). Egg consumption was positively associated with mortality because of all causes combined (in females), and cancers of the colon (in males and females combined) and ovary. Milk consumption was positively associated only with prostate cancer mortality, and cheese consumption did not have a clear relationship with any cause of death.

Please look at my answer at https://skeptics.stackexchange.com/a/2058/1403, where I deal with the math (a little) and describe the differences between correlation and causation.

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rajah9
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  • If two phenomena are correlated, then either one causes the other, or else they both have a common cause. Well, there is third possibility: that the correlation is a highly improbable statistical fluke. Ignoring that last one for a second, if we have credible studies that correlate cancer with meat eating, it's a little bit far fetched to suspect that there is a common cause: something mysterious that causes cancer, and that causes meat-eating behavior. – Kaz Apr 21 '12 at 05:02
  • @Kaz It's perfectly reasonable to suspect that people who decide to remove meat from their diet are also undertaking other pastimes (exercise, vitamins, sunlight, magnet bracelets, amulets, prayer...) which they regard as healthy, thereby decreasing their cancer risk regardless of meat's role. – Dave May 08 '12 at 18:20
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    @Kaz "something mysterious that causes cancer, and that causes meat-eating behavior." It might be e.g. income level, or a lifestyle, which can cause you to be more likely to eat meat, and to do other things which are unhealthy as well. – Suma May 09 '12 at 20:19
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    If these irrelvant variables are not accounted for with a control group, then you do not have a properly conducted experiment. This is the purpose of control groups: to eliminate the possibility that a variance in some other variable is actually causing variance in the variable of interest and that other variable is the ultimate cause. – Kaz May 09 '12 at 20:47
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    @Kaz, the Seventh-Day Adventist study will eliminate most of the other variables that Dave and Suma refer to, since you are getting a large group with similar religious beliefs and lifestyle. There is another possibility couched in the OP. It may be that the eating of meat does not cause cancer so much as the substitution of fruits and vegetables prevents cancer. I have read "Eat to Live" by Fuhrman (http://www.amazon.com/Eat-Live-Amazing-Nutrient-Rich-Sustained/dp/031612091X/ref=sr_1_1?s=books&ie=UTF8&qid=1336664609&sr=1-1) and this is his main thesis, and based on refereed medical journals. – rajah9 May 10 '12 at 15:46
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There are bunch of recent meta-analyses about red meat consumption and various cancers done by Alexander et al. Pretty much every one says the same:

Colorectal cancer and red meat

The available epidemiologic data are not sufficient to support an independent and unequivocal positive association between red meat intake and CRC. This conclusion is based on summary associations that are weak in magnitude, heterogeneity across studies, inconsistent patterns of associations across the subgroup analyses, and the likely influence of confounding by other dietary and lifestyle factors.

Colorectal cancer and processed meat

Overall, summary associations were weak in magnitude (i.e. most less than 1.20), processed meat definitions and analytical comparisons were highly variable across studies, and isolating the independent effects of processed meat intake is difficult, given the likely influence of confounding by other dietary and lifestyle factors. Therefore, the currently available epidemiologic evidence is not sufficient to support a clear and unequivocal independent positive association between processed meat consumption and CRC.

Breast cancer and red & processed meat

Overall, weak positive summary associations were observed across all meta-analysis models, with the majority being non-statistically significant. Heterogeneity was evident in most analyses, summary associations were sensitive to the choice of analytical model (fixed v. random effects), and publication bias appeared to have produced slightly elevated summary associations. On the basis of this quantitative assessment, red meat and processed meat intake does not appear to be independently associated with increasing the risk of breast cancer, although further investigations of potential effect modifiers, such as analyses by hormone receptor status, may provide valuable insight to potential patterns of associations.

Prostate cancer and red & processed meat

Similarly, no association with red meat was observed for advanced prostate cancer (SRRE = 1.01, 95% CI: 0.94-1.09). A weakly elevated summary association between processed meat and total prostate cancer was found (SRRE = 1.05, 95% CI: 0.99-1.12), although heterogeneity was present, the association was attenuated in a sub-group analysis of studies that adjusted for multiple potential confounding factors, and publication bias likely affected the summary effect. In conclusion, the results of this meta-analysis are not supportive of an independent positive association between red or processed meat intake and prostate cancer.

To reiterate all these papers have at least one researcher in common, so there is possible bias. Also I currently don't have access to full texts so I do not know the funding of these studies and I do not have the expertise to analyze the statistical side much.

Earlier study, Meat consumption and risk of colorectal cancer: a meta-analysis of prospective studies, by different researcher found that:

Consumption of red meat and processed meat was positively associated with risk of both colon and rectal cancer, although the association with red meat appeared to be stronger for rectal cancer. In 3 studies that reported results for subsites in the colon, high consumption of processed meat was associated with an increased risk of distal colon cancer but not of proximal colon cancer. The results of this meta-analysis of prospective studies support the hypothesis that high consumption of red meat and of processed meat is associated with an increased risk of colorectal cancer.

The possible cancer effects seem fairly small considering that the evidence is epidemiologic. The last paper I mentioned offers risk ratio of 1.28, so somewhat small increase. To put this into perspective CDC claims that smokers are 15-30 times more likely to get lung cancer compared to non-smokers.

Illotus
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