Red meat has been known to increase the risk of heart disease with its high saturated fats, but it’s also linked to higher cancer rates, and scientists didn’t know why until now. Researches from the University of California School of Medicine discovered what’s turning red meat into a cancer-causing food source, and published their findings in the journal Proceedings of the National Academy of Sciences.

When researchers took a closer look at red meat, they found the sugar molecule Neu5Gc may be the culprit. It’s found in most mammals except for humans, which is why when we ingest it our bodies it disrupts our system. Mice normally have Neu5Gc, but for the sake of the study researchers removed the molecule so the mice would mimic a human body. When they fed the mice the sugar molecule, they “significantly” developed cancer cells.

"Until now, all of our evidence linking Neu5Gc to cancer was circumstantial or indirectly predicted from somewhat artificial experimental setups," the study’s lead author Dr. Ajit Varki, professor of medicine and cellular and molecular medicine and member of the UC San Diego Moores Cancer Center, said in a press release. "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."

They examined the levels in different types of meat and found beef, pork, and lamb were rich in Neu5Gc. They were also the main sources of Neu5Gc for humans. They absorbed the sugar in through their bloodstream, which then transported it throughout the rest of the body. "Of course, moderate amounts of red meat can be a source of good nutrition for young people,” Variki said. “We hope that our work will eventually lead the way to practical solutions for this catch-22."

Red meat provides an enormous amount of protein and grass-fed cows are full of health omega-3 fatty acids. It's difficult to find such a nutrient-packed food source for our busy bodies. However, red meat could also contain a concoction of chemicals, hormones, and antibiotics that may or may not be worth it. But, the fact of the matter is that this newly-discovered sugar molecule caused spontaneous tumors formed five times as faster than mice that didn’t consume it. Their immune systems generated antibodies to fight the foreign Neu5Gc molecules, which caused inflammation known to fuel and accelerate tumor formations.

"The final proof in humans will be much harder to come by," Varki said. "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.”

Source: Varki NM, Samraj AN, Pearce OMT, Läubli H, Crittenden AN, and Bergfeld AK, et al. Proceedings of the National Academy of Sciences. 2014.