This week, Dr. Ajit Varki of the University of California at San Diego showed for the first time that feeding genetically-engineered mice a sugar called Neu5Gc, found in red meat, caused them to produce anti-Neu5Gc antibodies that caused spontaneous cancers (Proceedings of the National Academy of Sciences, published online Dec. 29, 2014).
Several previous studies have shown that eating red meat is associated with increased risk for cancers, diabetes and heart attacks (JAMA Internal Medicine, June 2013). Substituting other protein sources, such as fish, poultry, nuts or legumes, is associated with a reduced risk of death (Archives of Internal Medicine, March 12, 2012). However, epidemiological studies only show an association between eating red meat and cancers; they do not show that eating red meat causes cancer. This new study is the first to show that feeding a component of red meat to mice causes cancers. If future studies confirm this finding, I believe that Ajit Varki will be a strong candidate for a Nobel Prize in Medicine.
What is Neu5Gc?
In 1982, Varki discovered Neu5Gc, a sugar that is found in the meat from mammals but not in human cells, so any Neu5Gc found in humans comes from red meat that they have eaten. He proposed that when you eat red meat, the Neu5Gc from the meat is absorbed into your body and that this might explain why red meat is associated with increased risk of cancer. Much higher concentrations of Neu5Gc in humans are found in cancer cells with the highest concentration of Neu5Gc found in cancer tumors that metastasize (spread through the body and kill).
How Neu5Gc May Cause Cancer
Varki believes that your natural immunity attacks Neu5Gc in the same way that it kills germs that enter the body. When a germ gets into your body, your immunity recognizes chemicals on the germ’s cells that do not exist in your body and produces large amounts of protein antibodies that bind to germs and kill them. 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 that attach to and kill these cancer cells and they disappear from your body. If you do not produce antibodies to cancer cells, the cancer cells can grow and spread through your body.
Mice That, Like Humans, Do Not have Neu5Gc
Varki wanted to do studies to show how Neu5Gc could cause cancer in humans, but it is illegal and immoral to do cancer-causing studies on humans. He could not study any other mammals because the cells of all other mammals (except humans) contain Neu5Gc naturally, so they would not produce antibodies against Neu5Gc and therefore not cause cancer.
Ten years ago, a company in New Hampshire developed genetically-engineered mice that do not have Neu5Gc, so they could be used in Varki’s experiments. Because they have no Neu5Gc, they are like humans and different from all other mammals. Varki fed these mice Neu5Gc and like humans, the Neu5Gc stuck on their cells. Like humans, they developed antibodies against Neu5Gc.
Neu5Gc Causes Tumors in Mice
Dr. Varki had shown previously that giving Neu5Gc and antibodies to Neu5Gc to these genetically-engineered mice causes extensive cancers. Spontaneous tumor formation increased five-fold and Neu5Gc accumulated in the tumors in the mice. This new study showed that feeding Neu5Gc to the mice caused them to produce their own antibodies to Neu5Gc and they then developed extensive cancers.
What Does This Mean to You Now?
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, heart attacks and diabetes. This is the first study to show that a component of red meat, Neu5Gc, specifically causes cancers in mice. On the basis of this data, I recommend that you limit your intake of red meat.