Colon Cancer Risk and Neu5Gc Antibodies

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For many years I have been reporting on the work of Dr. Ajit Varki and others on Neu5Gc, a sugar-protein found in most mammals but not in humans, which may explain the association between eating red meat and increased risk for colon cancer (Genome Biol Evol, Jan 1, 2018;10(1):207-219). This week, researchers have suggested a method to measure antibodies in humans after they eat the foods that contain Neu5Gc (BMC Medicine, Oct 23, 2020;18(262)). They showed that:
• Mammal meat and dairy products contain a sugar protein called Neu5Gc that is not found in humans.
• After eating mammal meat or dairy products, humans react to Neu5Gc by producing the same types of antibodies that they produce to fight invading germs.
• The more meat and dairy a person eats, the higher the rise in antibodies against Neu5Gc.

The authors propose that they may be able to predict risk for developing colon cancer by measuring the amount of Neu5Gc in various foods, and the rise in blood antibody levels to Neu5Gc after eating these foods. They asked 19,621 study participants to keep food diaries to record how much mammal meat and dairy products they ate. Then they measured blood levels of antibodies against Neu5Gc and found that the blood levels of antibodies were driven by how much meat and dairy products they consumed. They developed a “G-cemic index” based on the amount of Neu5Gc in specific foods, which could potentially be used for future dietary recommendations to reduce cancer risk.

How Could Neu5Gc Increase Cancer Risk?
When people eat mammal meat or dairy products, Neu5Gc enters their cells. Your immune system recognizes germs that try to enter your body by certain surface proteins that are different from the ones you have in your body. Since humans don’t have Neu5Gc naturally, your immune system knows this is different from your normal cells and treats the Neu5Gc like an invading germ, producing antibodies that attach to and try to destroy the Neu5Gc. When your immune system is turned on and stays on all the time, it is called inflammation, which increases risk for cancers and heart attacks. Your own immune cells and chemicals can attach to and damage DNA in your cells to block apoptosis to cause cancers. They can also punch holes in in the inner walls of arteries to start forming plaques, which can break off from arteries to cause heart attacks. Eating a lot of Neu5Gc can cause the constant overactive immune system that causes inflammation and cell damage. Studies in mice altered to have immune systems like humans show that they develop cancer (Proc Natl Acad Sci USA, 2015;112:542–7) and heart attacks (Proc Natl Acad Sci USA, 2019;116:16036–45) when their antibodies against Neu5Gc rise from eating mammal meat. Humans who have high blood levels of antibodies against Neu5Gc appear to be at increased risk for colorectal cancer (PLoS One, 2018;13:e0197464).

My Recommendations
Every month I find new scientific articles that associate eating mammal meat with increased risk for obesity, diabetes, heart attacks and certain cancers. This recent article suggests that scientists can establish a measurement of mammal meats and diary products to show how much they may increase blood levels of antibodies against Neu5Gc. So far studies have not shown that people who eat red meat occasionally are at increased risk, but I think the data is strong enough to recommend that you limit your intake of meat from mammals and processed meats. Also see TMAO: Why Eating Meat or Eggs May Harm You
Meat Is Associated with Heart Attacks and Some Types of Cancer