Red meat has been linked to cancer for decades, with research suggesting that eating large amounts of pork, beef or lamb raises the risk of deadly tumors. But for the first time scientists think they know what is causing the effect: The body, it seems, views red meat as a foreign invader and sparks a toxic immune response.
In a new study, scientists from the University of California San Diego (UCSD) discovered that red meat contains a sugar that’s created naturally by many other meat-eating animals but not by humans. The sugar identified in the study, dubbed Neu5GC, caused tumors in mice genetically engineered to not produce the compound in a lab study conducted by the researchers.
The results, which are published in the Proceedings of the National Academy of Sciences, help provide a level of groundbreaking understanding about the cancer-causing effects of red meat consumption by humans.
“Until now, all of our evidence linking Neu5Gc to cancer was circumstantial or indirectly predicted from somewhat artificial experimental setups,” Dr. Ajit Varki, a professor of cellular and molecular medicine at UCSD, said in a press release announcing the breakthrough. “This is the first time we have directly shown that mimicking the exact situation in humans — feeding nonhuman Neu5Gc and inducing anti-Neu5Gc antibodies — increases spontaneous cancers in mice.”
However, adds Dr. Varki although Neu5Gc throws “gasoline on the fire,” it does not directly cause cancer in those who eat it. It is instead a catalyst of sorts for cancer: When eaten, the body sees it as a foreign substance – and the immune system attacks it. This leads to inflammation in the body, which over time is known to promote the formation of tumors.
In other carnivores the immune system does not kick in, because the sugar is already in the body. This answers the long-standing question of how other mammals can eat a diet high in red meat without any adverse health consequences.
The findings also diverge from a popular hypothesis that the higher risk of cancer associated with red meat consumption in humans comes from carcinogenic chemicals produced by grilling.
The study’s authors emphasize that moderate consumption of red meat does have nutritional benefits like providing protein, vitamins and minerals. Humans should eat 2.5 ounces or less of red meat per day, the equivalent of one lamb chop or two slices of roast beef, according to health experts.