red meat and knife As with many health issues, the problem with red meat is sugar and the body's reaction to a particular molecule. (Photo: Ronald Sarayudej [CC BY 2.0]/Flickr)

Health experts have known for years that the consumption of red meat raises a person's cancer risk, but it took time to understand why.

Turns out it's not the fat in red meat that increases cancer risk. Nor is it the cholesterol or the way we grill our burgers and steak. It's the sugar.

Researchers at the University of California, San Diego discovered that the reason red meat is linked to higher cancer risk is that it contains a sugar molecule — specifically Neu5Gc — that's not naturally found in the human body. When the immune system spots this sugar molecule, it attacks it, and it's inflammation from this attack that, over time and continued exposure, raises a person's lifetime risk for cancer.

What's more, Neu5Gc is found in beef, pork, lamb and bison. However, it's not found in chicken or fish — two sources of meat that aren't linked to an increased cancer risk. It's also found in fish eggs (caviar,) as well as whole milk and certain cheeses.

Previously, health experts believed that it was the grilling of red meat that led to the increase in cancer risk. But researchers couldn't understand why grilling chicken and fish didn't also lead to an increased risk. Now, they have a better understanding of why.

charcoal grill Contrary to popular belief, it's not your grill that increases the cancer risk of eating red meat. (Photo: senk/Shutterstock)

Dr. Ajit Varki, the lead author of the study, said the Neu5Gc phenomenon is unprecedented, explaining that Neu5Gc is the "gasoline on the fire" — meaning it doesn't directly cause cancer, but it boosts the risk for the disease. Varki explains in an in-depth interview with the San Diego Union-Tribune:

"In this case, the foreign sugar is like a Trojan Horse. It becomes part of your own cells," he said. "When you react to a peanut or other allergy-causing substance, you’re reacting to something foreign. This is the first example we know of something that’s foreign, gets totally incorporated into you despite the fact that your immune system recognizes it."

The study was published in the Proceedings of the National Academy of Sciences.

What about chicken?

roasted whole chicken Roasted chicken is easy to make — and it gets points from these medical studies. (Photo: Africa Studio/Shutterstock)

For those wondering if they should stop eating red meat? Varki doesn't think so. He recommends using moderation when choosing red meat and limiting consumption to two or three servings per week. Interestingly, Varki doesn't eat meat himself, but he does eat poultry and fish. A more recent study may give credence to his approach.

Researchers working with Dale Sandler, PhD, of the National Institute of Environmental Health Sciences, found while eating red meat may increase the risk of breast cancer, eating poultry has the opposite effect. Their work was published in International Journal of Cancer.

They followed the meat eating and cooking practices of 42,012 women — part of the Sister Study, which studies sisters and their breast cancer link— who were followed for an average of 7.6 years. The contrast was clear, according to Science Daily: Those who ate the most red meat had a 23% higher risk when compared with those who consumed the least. On the other side of the equation was similar: Those who at the most poultry had a 15% lower risk than those who ate the least.

Sandler said they don't know why the poultry had such a positive effect, but even without that information, it's becoming clearer that eating less red meat or eliminating it may reduce your cancer risk.

Editor's note: This story has been updated with new information since it was published in January 2015.

Why red meat raises your cancer risk
The reason red meat is linked to higher cancer risk is that it contains a sugar molecule called Neu5Gc that isn't naturally found in the human body.