A new research review may make you think twice before ordering the steak special. Researchers have found an association between eating processed meat or red meat and an increased risk of colorectal and other cancers. The review was performed by 22 researchers from ten countries who worked on behalf of the International Agency for Research on Cancer. It was published in the journal Lancet Oncology and included an assessment of over 800 studies that investigated the relationship between cancer and the consumption of red meat (such as beef, veal, pork, and lamb) or processed meat (meat that has been salted, cured, fermented, smoked, or otherwise processed for preservation and flavour-enhancement). The 800 studies involved people from a few continents, with diverse ethnicities and diets. Researchers defined the most informative studies as those that analysed red and processed meat separately, had dietary data from validated questionnaires, included a large number of participants, and controlled for other major factors that may contribute to cancer risk. Here is what they found in their review:

• In a meta-analysis of ten cohort studies (a type of observational study), the risk of colorectal cancer increased by 17% for every additional 3.5 ounces of red meat consumed per day (compared with eating no red meat), and by 18% for every additional 1.8 ounces of processed meat consumed per day (also compared with eating no processed meat). Roughly speaking, 4 ounces of meat might be the size of a deck of cards.
• In a 2013 meta-analysis, there was a statistically significant association between eating red or processed meat and benign tumours of the colon and rectum.
• In two intervention studies, consuming between 10.6 and 14.8 ounces of red meat per day increased the levels of potentially cancerous cells in participants’ colon and rectal biopsies.
• In cohort studies and population-based case-control studies, there was an association between the consumption of red meat and an increased risk of cancers of the pancreas and prostate, and an association between the intake of processed meat and an increased risk of stomach cancer.
• Meat consumption varied largely by country; however, in countries where people did eat red meat, they ate an average of 1.8 to 3.5 ounces per day. Information regarding processed meat consumption was not available.

Based on the large amount of evidence supporting the association between processed meat and colorectal cancer, the researchers classified processed meat as “carcinogenic [cancer causing] to humans.” They classified red meat as “probably carcinogenic to humans.” In other words, the risk is stronger for processed meat. This might be due to the fact that curing and smoking meat, among other processing techniques, can cause the formation of carcinogenic substances. However, cooking red meat, especially over high temperatures (like saucepan-frying or grilling), can also produce known or suspected carcinogens. Therefore, limiting processed meats and avoiding cooking red meat until it's “well-done” can help decrease exposure to these carcinogens. Nevertheless, not everyone agrees that the risk from eating meat is substantial. While the evidence appears to consistently show that red meat raises one's risk of certain cancers, the absolute increase in risk is likely small, especially if you are otherwise fit, don’t smoke, exercise regularly, aren’t overweight, and don’t drink excessively.

Source: Lancet Oncology