It has been known for some time that consuming large quantities of red meat increases the risk of developing certain cancers. However, the cause of the relationship between red meat and cancer risk had never previously been determined.  Researchers at the University of California, San Diego School of Medicine think they may have found the answer.

The researchers turned their attention to Neu5Gc, a sugar molecule naturally found in most mammals but not humans. The team had previously determined that Neu5Gc can be absorbed by human tissue. However, since the molecule is foreign to human anatomy, it triggers an inflammatory response. The team then hypothesized that red meat would cause chronic inflammation, a response known to promote tumor formation.

To test this hypothesis, the researchers engineered a group of mice that did not naturally produce Neu5GC to represent humans. The test group was then fed a diet rich in Neu5Gc. Without their bodies naturally producing the sugar, their immune system developed antibodies against it. The test group developed systemic inflammation and spontaneous tumor formation became five times more common. The Neu5Gc was found to be accumulating in the tumors.

The study featured no other known carcinogens or artificially induced cancers, further solidifying the relationship between the sugar and the tumors.

“Until now, all of our evidence linking Neu5Gc to cancer was circumstantial or indirectly predicted from somewhat artificial experimental setups,” said Ajit Varki, the lead author of the study, in a statement. “This is the first time we have directly shown that mimicking the exact situation in humans — feeding non-human Neu5GC and inducing anti-Neu5Gc antibodies — increases spontaneous cancers in mice.”

The team examined samples of common foods and found that beef, pork, and lamb were rich sources of Neu5Gc. This affirmed that foods of mammalian origins are the primary sources of the sugar molecule in the human diet.

“The final proof in humans will be much harder to come by,” said Varki. “But on a more general note, this work may also help explain potential connections of red meat consumption to other diseases exacerbated by chronic inflammation, such as atherosclerosis and type 2 diabetes.”

Varki noted that red meat in moderation is not necessarily bad for your health.

“Of course, moderate amounts of red meat can be a source of good nutrition for young people. We hope that our work will eventually lead the way to practical solutions for this catch-22.”

The original study was published online in the early edition of Proceedings of the National Academy of Sciences.  The full statement is available here.