Georgofili World

Newsletter of the Georgofili Academy

Considerations on the carcinogenicity of red and processed meat

The Associazione Scientifica per la Scienza e le Produzioni Animali (ASPA) has for some time had a study committee to assess the level of knowledge on the relationship between foodstuffs of animal origin and human health, to identify possible areas deserving attention and in-depth study, and to foster dialogue with the entire scientific community by promoting accurate information on this topic. It is this very aspect of communication that, in the recent days, has been the focus of great concern to the entire scientific community that deals with animal-derived foodstuffs because of the intense media campaign that has followed the publication in the scientific journal Lancet Oncology of a brief note by the International Agency for Research on Cancer (IARC) working group. In fact, a few days ago, IARC issued a report not yet available that, however, was summarized in a short two-page note published in the news section of the journal Lancet Oncology, where 22 scientists consider to be carcinogenic to the colon and rectum the consumption of processed meats and probably carcinogenic that of red meat.
Although acknowledging the high nutritional value of meat, the panel’s response has led IARC to classify processed meats in group 1 (carcinogenic substances for humans) and red meat in group 2A (probably carcinogenic substances for humans) as regards colorectal cancer (CRC). The panel made this majority decision on the basis of the analysis of about 800 publications, as stated in the note, only 27 of which, however, were about processed meats (12 positive responses in 18 publications on epidemiological studies and 6 positives out of 9 in control-cases for a total sum of 18 positives out of 27, equal to 67%) and 29 about red meat (7 positive responses out of 14 publications in epidemiological studies and 7 positive out of15 in control-cases for a total sum of 14 out of 29, equal to 48%). Moreover, the panel also supplied, on the basis of assessments/evaluations carried out in a single meta-analysis, the dose/response risk quantifying it equal to an18% increase in CRC for every 50 grams of processed meats consumed daily and 17% per 100 grams of red meat consumed daily. However, only a year ago, another group of 23 scientists from 8 countries concluded that the relationship between the consumption of processed meats and fresh red meat and CRC are inconsistent. It is the opinion of the authors of this note that this is a highly controversial issue (a fact confirmed by the IARC panel not achieving consensus in issuing the opinion and by a totally opposite response published by Oostindjier et al. in 2014). Much more evidence is needed beyond what was used by the IARC to be able to state with certainty that the consumption of such a complex food is definitely linked, albeit with very low levels of risk (1/10 that of smog exposure, 1/20 of alcohol consumption, and 1/30 of smoking cigarettes) to the onset of colorectal cancer. Moreover, the reason remains unclear as to why the framers of the note cited, in support of its opinion on processed meats and red meat, cited the results of a very important epidemiological study like the EPIC one, first published 10 years ago, and not the results of the EPIC study updated in 2013. On the one hand, the latter study confirmed the association between processed meat consumption and colorectal cancer (for those who ate 160 grams per day of processed meats compared to those that ate less than 20 grams per day). On the other hand, however, it was clearly pointed out that such an association does not exist for red meat. Basically, the very scientific literature used to support the opinion is far from being univocal in indicating an association/correlation between red meat and CRC. In addition, as regards processed meats, despite the experimental evidence being more relevant, considerable uncertainty remain, at least as regards the quantity to be consumed in relation to the CRC risk. This contradiction also comes out in the text of the note published in Lancet Oncology, where the authors declare on the first page that the literature contains very limited experimental evidence on the carcinogenicity related to the consumption of red meat, except for concluding, at the end of the note, that the evaluation of the carcinogenicity related to the consumption of red meat is supported by relevant literature data including substantial epidemiological data. It is therefore impossible to understand whether the literature containing the experimental evidence on this aspect of the carcinogenicity related to the consumption of red meat is limited or relevant and substantial. Given the lack of clearness by the note’s authors, it is not surprising that mass media caused even greater confusion when it stated that both processed and red meat were definitely carcinogenic.
Finally, the view is shared that Italian meat chain controls are sufficient to protect the consumer from the toxicological risks relative to the consumption of fresh and processed meats. Besides, it must not be forgotten that many salamis marketed in Italy, especially the PDO raw hams, do not contain some of the substances considered potentially carcinogenic for processed meats, i.e., the nitrates and nitrites often used as preservatives. This aspect too should be carefully evaluated before launching blanket alarms on the consumption of whole categories of food. In this regard, it is useful to point out that the note in Lancet Oncology began by recalling that processed meats contain substances suspected of being carcinogenic agents, like compounds deriving from nitrates and nitrites (NOC) and polycyclic aromatic hydrocarbons  (PAHs). Even if definite data on the cause-effect relationship between the content of these substances in processed meats and the increase in CRC incidence found in the epidemiological studies are not available, the fact that  NOC and PAHs are present in processed meats, together with the results of a part of the 27 studies analyzed seems to be sufficient to justify the inclusion of these foodstuffs in the group of certainly carcinogenic substances, like asbestos and cigarette smoke (for which, on the contrary, there exist proven studies of cause-and-effect ). However, there is considerable uncertainty even on the actual toxicity of NOS, as some studies suggest that  nitrates and nitrites can also be metabolized as nitric oxide and as such promote a cardiovascular benefit. Moreover, it is known that processed meats are not the only sources of NOC and PAHs in the human diet. In fact, many kinds of fresh vegetables (carrots, spinach, cabbage, rucola, etc.) are important sources of both NOC and PAHs, while baked goods, various kinds of drinks, and shellfish are certainly primary sources of PAHs.