Some recent claims have warned about a link between eating red and processed meat and the risk of developing cancer.  While vegetarians unleashed their confirmation bias in full force, they were happy to ignore the uncertainties in the evidence.

As often happens, concerns about reports, rather than data, lead to action and there have been called for new nutritional recommendations cautioning people to limit their intake of red and processed meats. A recent review in Meat Science examines the evidence and seeks to improve the foundation for future recommendations on the intake of red meat.

No one advises a human diet solely of red or processed meat. Yet in animal studies that is entirely possible and it is possible to promote cancer by giving the animals a chemical cancer challenge and a basic "standard" diet that is high in meat, without any ingredients that protect and can help the gut stay healthy. This means no vegetables, no fiber, no milk or other sources of calcium.

In other words, the "standard" diet of the lab animals is not comparable to that of humans.

In humans, the observed association between red and processed meat intake and cancer is relatively small in magnitude, but consistent, and may still present a serious public health impact - that is why you shouldn't eat one thing, including just vegetables. The 23 authors of the new review conclude that other foods, in cooperation with the bacteria that live in the gut, may protect the gut so any potential adverse effects of meat may become less pronounced or may even be fully prevented.

Suggested mechanisms for potential health risks of red and processed meat consumption. Nitrate and nitrite in meat are metabolized to nitrogen oxides, which in turn react with secondary amines in the stomach to form N-nitroso compounds (NOC). These NOC are implicated in increased CRC development. Haem iron can catalyze this formation of NOC in the stomach. Haem iron also can react with polyunsaturated fatty acids in the gut, resulting in Reactive Oxygen Species (ROS) that can damage DNA and disrupt normal cell division. Abnormal gut bacteria and an unbalanced diet are also implicated in a higher risk for CRC development through an increase in gut inflammation. Credit: 
DOI: 10.1016/j.meatsci.2014.02.011

The scientists further concludes that science does not yet have a full understanding of how food that we eat affects our gut and our health. To get a better grip on this complex issue, it is necessary that improved measures of how much meat people eat, the composition of the meat they eat, and how this affects the risk that cancer develops.

Citation: Marije Oostindjer, Jan Alexander, Gro Vang Amdam, Grethe Andersen, Nathan S. Bryan, Duan Chen, Denis E. Corpet, Stefaan De Smet, Lars Ove Dragsted, Anna Haug, Anders H. Karlsson, Gijs Kleter, Theo M. de Kok, Bård Kulseng, Andrew L. Milkowski, Roy J. Martin, Anne-Maria Pajari, Jan Erik Paulsen, Jana Pickova, Knut Rudi, Marianne Sødring, et al., The role of red and processed meat in colorectal cancer development: A review, based on findings from a workshop', Meat Science, Feb 24 2014 DOI: 10.1016/j.meatsci.2014.02.011