Earlier this year, the World Health Organization's International Agency for Research on Cancer added processed meat to its list of potentially carcinogenic foods, and red meat to its list of foods that are likely to be carcinogenic foods. As a result, processed meat was placed in the same category as some of the most harmful chemicals for human health, such as nicotine, alcohol, and even nuclear material. This decision sparked an instantaneous outrage, and oversimplified interpretations abound, including criticizing the link between the key component of nuclear weapons and a hamburger, as well as saying that tobacco and bacon are both as harmful. Because meat affects components of many people's identities that go far beyond their nutritional value, it has continued to garner attention in the public discourse since then. Also contributing to its intricacy, relevance, and emotional intensity are the high levels of CO2 emissions involved with its production (particularly in the case of beef), as well as concerns about animal welfare.

Researchers from the University of Oxford have published a study in the journal BMC Medicine today in which they examine the association between varying amounts of meat intake, fish consumption, and a vegetarian diet with the risk of developing cancer. It was the Spanish Aurora Pérez-Cornago who served as the team's principal investigator, and they used information compiled by the United Kingdom Biobank, a repository that contains information of medical interest from half a million volunteers, ranging from data on lifestyle or electronic health records to genome data or your cardiovascular health, to conduct their analysis.

Data from 472,377 persons between the ages of 40 and 70 years old were used from a total of half a million people in the biobank. Of them, 247,571 (52 percent) consumed meat more than five times a week, 205,382 (44 percent) had meat five times a week or less, 10,696 (2.2 percent) consumed fish but not meat, and 8,685 (1.8 percent) consumed meatless diets. A total of 54,961 people (12 percent) developed cancer over the course of the study's 11-year follow-up period. Individuals who consumed meat five times or less per week had a 2 percent lower risk of having a tumor than those who consumed meat five times or more per week, according to the study. The risk of heart disease was 10 percent lower in individuals who ate fish but not other meats. Dietitians and vegans had a 14 percent lower risk of heart disease.

The research also looks specifically at the most frequent cancers (colon, prostate, and breast), which account for 39 percent of all tumors in the United Kingdom. Men who ate fish but not meat had a 20 percent lower risk of prostate cancer, while vegetarians and vegans had a 31 percent lower risk of prostate cancer than men who ate meat. In this study as well, vegetarian women were shown to have an 18 percent lower risk of breast cancer than women who ate meat more than five times a week, but the difference was attributed to the higher body mass index of carnivores and the fact that obesity is a risk factor for these diseases.

The findings of this observational study are consistent, at least in terms of trend, with the findings of many other studies that have attempted to determine the impact of food in tumor growth. However, it does have some limitations, same as the other research. The authors express caution in their conclusions, stating that the nature of their research does not allow for the establishment of a cause-and-effect relationship between diet and cancer risk.

Marina Pollán, director of the National Center for Epidemiology, reminds out that it is difficult to draw clear and solid findings from this type of study. According to her, "that happens with practically all risk estimators when you study lifestyles, with the exception of items such as tobacco, which is a total carcinogen." "Dietary research is difficult since it is done through a questionnaire on the frequency with which a food is taken, and it is difficult to complete these surveys," says the researcher. To get the best results, you must do a mental extrapolation in which the outcomes are predetermined." According to Pollán, this gives the impression that the outcome of this type of study is less conclusive than it actually is.. We have observed in epidemiology that these types of questionnaires have a tendency to underestimate the true impact of things like food," she continues.

The epidemiologist asserts that the organisms that rely on this type of information to generate dietary recommendations or warnings are "very cautious," and that they contribute to the observation in humans toxicological studies or with animals that can be more controlled than they are in animals. In contrast to humans, who are unable to regulate all aspects of their lifestyle or the amount of food they consume, this can be accomplished in mice, and the results indicate that certain goods, such as processed meat, may provide a carcinogenic danger to these animals. Pollán believes that "the recommendations are reasonable" in any circumstance. As she points out, "it is not said that one should abstain from meat eating; rather, it is stated that one should restrict meat consumption." The fact that if you consume a lot of meat, you will cease eating other things like beans or fish, is also interesting."

However, despite widespread support for dietary recommendations such as those issued by the World Health Organization, there are some scientists who are skeptical, believing that evidence from observational studies does not provide sufficient certainty and that the results of animal studies cannot be applied to humans directly. Despite the fact that "the impact in these trials is repeated," Pablo Alonso Coello, a researcher at the Ibero-American Cochrane Center (IIB Sant Pau) in Barcelona, points out that the effect "is extremely tiny." As he explains, "This type of research can assist in making firmer recommendations if the effects shown are significant, as was demonstrated by the link between cigarettes and cancer, but not as was demonstrated by the relation between meat consumption and cancer."

According to the journal Annals of Internal Medicine, Alonso Coello signed a long and contentious evaluation of this sort of study on the relation between meat consumption and cancer in 2019. The review was published in 2019. It said that the certainty of the evidence linking meat consumption to cancer was either low or extremely low, depending on the source (for processed meat the certainty is moderate). Following these kinds of findings, the researcher believes that it is necessary "to condition or weaken the recommendation to consume less meat." Fortunately, colon cancer is a rare disease. " He goes on to say, "What we discover in this study is that the low risk may be lowered to a somewhat smaller size, but the change in risk is very small, and the certainty of that information is also very modest."

The researcher also believes it is critical to distinguish between what information means from the perspective of public health and what information means from the perspective of the individual. At the population level, something that does not represent a significant difference in risk for a single individual can represent a significant variation in risk for many individuals. The precautionary principle is applied extensively in this diet, according to the author, who notes that despite the uncertainty, several suggestions are offered.