It's a common topic among the vegan community; meat causes cancer. While there are plenty of studies to show a positive association between high protein intake and cancer, biology doesn't often have such a simple conclusion. Let's dig a bit deeper, shall we?
The studies often referenced are of mouse studies using a high dosage of methionine, an amino acid found in meat. These studies find a correlation between high methionine diets and cancer incidences. Conversely, when the diets were adjusted to include glycine, or collagen, the correlation was nonexistent.
Study: https://www.ncbi.nlm.nih.gov/pubmed/3668700
While processed meats commonly found in the Standard American Diet are high in methionine and low in glycine, this wasn't always the case.
Our early ancestors made use of every part of the animal, not just the choice cuts of meat like we eat today. Cartlidge and connective tissue are rich sources of glycine, which we need to rebuild our own connective tissue like tendons and joints. Bone broth is also a great source of glycine, broth being much more common in our diets 70 or 80 years ago and undoubtedly more so before that. Again, when we often utilized every part of an animal rather than buying one or two peices.
To quote my previous article on healthy food being too expensive: "Evolution set us up for this. Having large amounts of a single nutrient throws us off balance. It's like the difference between eating an orange and drinking a large soda. The Orange has fiber, vitamins, minerals, phytonutrients and a small amount of sugar. The soda is mostly pure sugar and some artificial flavorings. Taking it in from such a concentrated source causes a huge blood sugar spike, fat storage and inflammation." Our bodies do much better avoiding processed foods, and running mostly on whole-food sources. Complete foods are more easily digested and assimilated because they have all of the nutrients that are expected to come together, not just one or two. Adding bone broth, collagen or just eating cuts of meat with more connective tissue such as leg of lamb will re-establish a balance between glycine and methionine.