Red Meat’s link to Cancer: An Inflammatory Response

The short answer is, non-human sialic acids. These are the presumed culprits behind red meat’s link to cancer.

But before we delve into some molecular and evolutionary biology let’s set the record straight. When discussing “breaking news” a healthy dose of skepticism is the best potion, as there has been instances where these shocking breakthroughs report nothing more than the findings of a single study, in many instances these single studies are not even reproducible and have limitations of their own (e.g., small sample size). Valued scientific reports are those that encompass the systematic consolidation of the totality of evidence. Perhaps now you have an idea as to why we often hear that so many different things cause cancer, exactly, the answer is: irresponsible science reporting. Overall, these kind of faulty breakthroughs actually endangers the trustworthiness of the scientific community in the general public by perpetuating false assumptions.

This is your one paragraph crash course in high school biology… I know, I know, just stay with me. If you recall, cells have a funny looking structure called the rough endoplasmic reticulum or rough ER for short. The rough ER is where messenger RNA delivers its message so that ribosomes attached to the ER can make the proteins our body needs to carry on with normal cellular day-to-day activities, this process involves the polymerization of amino acids into long chains (50 or more amino acids constitutes a protein). But another important role performed by the ER is the glycosylation of newly synthesized proteins, i.e., the process of sugar attachment into new proteins. These sugars come in two forms O-linked and N-linked and have sialic acids at their distal ends; human sialic acid is Neu5Ac also known as NANA. For simplicity, we will skip all the hefty details of synthesis and jump straight to the fully synthesized sugar-protein with the sialic acid attached at its distal end. These proteins containing sialic acids are transported and incorporated into the outer membrane of every cell in your body. Sialic acids are primarily associated with adhesion molecules (e.g., integrins, selectins) in the outer surface of cells. These adhesion molecules have many roles; one in particular is the process of diapedesis, where immune cells move from the circulation into the site of infection to fight pathogens, immune cells accomplish this by attaching to these adhesion molecules and squeezing through endothelial venules. Furthermore, another example includes red blood cells, here sialic acids work like a time-clock signaling how old the cell is. In general, the less sialic acid a red blood cell has the older it is (red blood cells have a lifespan of about 120 days), and as it turns the older the red blood cell is, the more likely it is to be transported to the liver for dismantlement and recycling of its iron and amino acids, the remaining carcass is then excreted in the urine and feces (dead red blood cells are what gives urine and poop their unique color). There is no doubt sialic acids play a crucial role in our biology in guiding the day to day activities within our system. So what’s the problem with these so-called sialic acids?

Well, as it turns out, some time ago we found that certain viruses like influenza, adenovirus, rotavirus, and the malignant measles among others use sialic acids as means of entry into cells. Long time ago, deep in our evolutionary history our ancestor cells also expressed the cousin of our current sialic acid, his name was Neu5Gc (recall from earlier that our sialic acid is Neu5Ac, just a letter difference!). It is believed that a deadly form of measles used Neu5Gc as means of entry and so about 3 million years ago the bodies of our ancestors adapted to the viral threat by eliminating the gene that codes for this form of sialic acid, CMAH. This allowed our ancestor to thrive in an environment where pathogenic threats were always on the periphery, in this particular case by inhibiting the entrance of the deadly measles virus.

Today we are well aware that other mammals still exhibit the Neu5Gc form of sialic acid. In 2001, Ajit Varki medical doctor and research scientist at UCSD carried out an experiment where he ingested 150mg in the form of a “pig-spit Slurpee” (sialic acids are abundant in saliva) and tested his blood for elevated levels of this so called non-human sialic acid. Over the next weeks, the levels of Neu5Gc in Varki’s urine, saliva, and hair increased. It was in fact becoming part of his cells. Other researchers have performed the same experiment and yield similar results since. But the big problem is that this form of sialic acid carries an extra oxygen that our immune system recognize as foreign and so it devices an attack against it, thus causing inflammation.
In the words of Rob Dunn Evolutionary Biologist at North Carolina State university and author of The Man Who Touched His Own Heart, “people who eat mammal meat [(beef, pork, lamb)] incorporate the sugar from the meat into their cells. The body’s immune system sees the sialic acids on the tips of these sugars as foreign, and it attacks, a reaction that occurs throughout the body, including the arterial walls.”

Just over a month ago around October 26th the media blew up with articles linking red meat to cancer. It makes perfect sense, the science appears to be conclusive and I am sure more studies are on the way, as you know such claims can’t be made against normal sugar and vegetable oils (I’ve seen it in the headlines) because there are simply no well-designed studies to corroborate those conclusions. Finally, here is the suggestion of The American Institute of Cancer Research, which recommends a diet of no more than 18 ounces of cooked red meat per week to decrease the risk of colorectal cancer.

I hope you found this blog informative as well as entertaining. I enjoy writing about these topics because I often find myself wondering the “why” of things and well, it helps my writing skills too; but as always, leave you kudos, subscribe, say hello, send me comments, complaints, suggestions, but most importantly spread the information! Until next time.

Mounir C. Cejin.