This year, researchers have identified the CMAH gene in meat, dairy, and even caviar from some fish that produces a sugar-protein called Neu5Gc, which may explain the association between eating red meat and increased risk for certain cancers (Genome Biol Evol, Jan 1, 2018;10(1):207-219).  Epidemiological studies show that eating red meat (beef, pork, and lamb) is associated with increased risk for some cancers and other diseases.  Researchers followed 536,000 men and women, ages 50 to 71, for an average 16 years and found that those who ate the most meat from mammals and processed meat had a 26 percent greater risk of dying within the study period than those who ate the least (Brit Med J, May 9, 2017). High mammal meat consumption was associated with increased rates of death from cancer, heart disease, respiratory disease, stroke, diabetes, infections, kidney disease and liver disease. The study was supported by the U.S. National Institutes of Health (NIH) and the National Cancer Institute (NCI).
Neu5Gc and Risk for Cancer
We do not have an explanation for the association between eating meat from mammals  and various diseases in humans, but a leading theory was offered by Ajit Varki in 1982 when he discovered a sugar-protein on the surface of all cell membranes in mammals except humans.  He called this sugar-protein Neu5Gc, and in 2014, he published data showing how Neu5Gc may cause cancer (Proceedings of the National Academy of Sciences, published online April 7, 2014).
He explained that when you eat red meat, the Neu5Gc from the meat is absorbed into your body and your body treats this sugar-protein in the same way that it treats germs that try to get into your cells.  Your immunity recognizes germs by the sugar-proteins on the surface of their cells.  If the surface proteins are the same as those on your cells, your immunity lets the protein enter you cells, but if the surface proteins on membranes are different from those on your cells, your immunity tries to kill the invading germs.
The same applies to cancer cells.  Every day, your body produces millions of cancer cells. Your immunity recognizes cancer cells as being different from normal cells and produces antibodies and cytokines that attach to and kill these cancer cells. This is exactly the same mechanism that your immunity uses to try to prevent germs from growing in your body. If your immunity produces large amounts of antibodies against cancer cells, you kill them and they disappear from your body.  If you produce only small amounts of antibodies to cancer cells, the cancer cells can grow and spread through your body.
How Neu5Gc May Cause Cancer
All mammals except humans have Neu5Gc on the surface of their cells. Humans receive Neu5Gc only when they get it from eating meat or dairy products from mammals. When you eat red meat, you absorb Neu5Gc into your body and your immunity treats the sugar-protein as a germ that is trying to attack your body.  For more than 30 years, Varki has wanted to do studies to show how Neu5Gc could cause cancer, but it is illegal and immoral to do studies that cause cancer in humans. Ten years ago, a company in New Hampshire developed mice that do not have Neu5Gc for use in Varki’s experiments. Because they have no Neu5Gc, they are like humans and different from all other mammals, and their immunities recognize Neu5Gc as an invading germ. Varki took these mice and fed them Neu5Gc. The mice immunities treated Neu5Gc from red meat just as those of humans would do.  Their white blood cells and cytokines attacked the Neu5Gc as if it was an invading germ. Then he gave the mice antibodies that attach to and try to destroy Neu5Gc. When he gave them low doses of antibodies against Neu5Gc, tumors developed and grew rapidly. In mice who were given high doses of antibodies, the antibodies attached to and killed the tumors. He feels that when your immunity is working properly, it produces enough antibodies to kill the cancer cells. However, if your immunity produces only small amounts of antibodies, it appears that cancer cells are able to grow and spread through your body.
How Varki Found Neu5Gc
Varki ground up cow’s muscle and put it into a 20-foot column of gel with a positive charge on one side and a negative charge on the other. This separated out almost 1500 different protein and sugar molecules. He did the same with human muscle. He found a sugar-protein in cow’s muscle that was not in human muscle, and called it Neu5Gc. He explains that at one time, all mammals had Neu5Gc on their cells. However, a mutation occurred in humans that converted Neu5Gc to another sugar-protein that he called Neu5Ac. Today all mammals except homo sapiens have Neu5Gc. Humans have Neu5Ac in its place.
Varki’s Explanation of How Red Meat Could Cause Cancer
Many studies show that people who eat red meat or dairy products have Neu5Gc on their cells. Much higher concentrations of Neu5Gc in a human’s body is found in cancer cells with the highest concentration of Neu5Gc in humans found in cancer tumors that metastasize (spread through the body and kill). If you have a strong immunity, your body will produce very large amounts of antibodies against Neu5Gc and you will kill the cancer cells. However, if your immunity does not produce enough antibodies against Neu5Gc, the cancer cells can grow, and can spread through your body. Varki is now trying to cure cancers by working on ways to increase antibody production.
My Recomendations
Not everyone agrees with Varki’s ideas about Neu5Gc and cancers, but there is strong evidence linking red meat and some types of cancer, particularly colon cancer. Epidemiological data show that people who eat red meat daily are at increased risk for many cancers, but the data fail to show that people who eat red meat once a week or less are at increased risk. On the basis of this data, I recommend that you limit your intake of red meat and dairy products.