Diets high in red and processed meat have long been shown in epidemiological studies to be associated with increased cancer risk. The World Cancer Research Fund/American Institute for Cancer Research (WCRF/AIRC) labeled processed meat as a “probable carcinogen” and red meat as a “possible carcinogen” based on an extensive analysis of the literature. Using only those studies that met the rigor of inclusion, 19 of 33 studies showed a link between increased cancer risk and the consumption of red or processed meat.
While this was a majority of the studies, a fairly substantial number (14 of 33) failed to show a statistically significant association. Furthermore, while red meat was categorized as a cancer risk in the same category as asbestos and cigarettes, the degree of risk is orders of magnitude different—the increased hazard from processed meat was 0.18 fold compared with cigarettes at more than 20 fold.
The other significant problem in assessing cause of disease with diet is that if one constituent goes up another goes down. This is coupled with the fact that epidemiological studies are fraught with confounding findings, some—but not all—of which can be accounted for in the analysis.
A recent meta-analysis showed that the Western dietary pattern (high in processed and red meat, high fat dairy products, fast food, refined grain, coffee, sugary drinks, and desserts) is associated with increase colorectal cancer (CRC) risk. But, to determine causality, further probing is needed to test whether meat and processed meat are the only culprits or whether it might be other lifestyle and dietary factors associated with meat eaters.
There also needs to be consideration for what is omitted, which can be at least as problematic as what is included. For example, in a recent study of a 30-year prospective cohort of more than 10,000 Dutch men and women, the CRC risk of vegetarians, pescetarians, and those who eat meat once in a week showed a non-significantly decreased risk compared to those who eat meat 6–7 times a week. The authors noted that the difference in risk was due to dietary constituents other than meat and specifically named lower dietary fiber (DF) and legume intakes.
Often, those with high meat consumption (Western diet) have low consumption of fruits, vegetables, nuts, legumes, and whole grains, which lowers their intake of components known to be associated with lowered cancer risk such as DF, resistant starch, vitamins, minerals, and phytonutrients. In addition, obesity and a sedentary lifestyle can increase the risk of CRC.
So, before meat is banished from plates, perhaps it is time to reconsider the important nutritional watchwords of balance and moderation. The problem I would argue is an overall imbalance with too much of some foods and not enough of the others.
Julie Miller Jones, PhD, CFS
Distinguished Scholar and Professor Emerita of Foods and Nutrition
St. Catherine University