In 2001, Ajit Varki drank a bunch of pig spit. What does drinking the extraction of pig salivary glands give you? Sialic acid, something every mammal in the world produces except humans. Why are we left out?
MANY people have been making the case that Americans have grown fat because they eat too much starch and sugar, and not enough meat, fat and eggs. Recently, the Dietary Guidelines Advisory Committee lifted recommendations that consumption of dietary cholesterol should be restricted, citing research that dietary cholesterol does not have a major effect on blood cholesterol levels. The predictable headlines followed: “Back to Eggs and Bacon?”
These are not controlled studies. While controlled studies provide better evidence, they are not feasible for all questions (in this case it would be impractical and unethical). Results from observational studies like this one are not invalid, you just need to consider potential confounding, as they seem to have done here. The study itself says that substituting fish, poultry, and nuts for red meat lowered the mortality risk.
This is no surprise coming from Dr. Dean Ornish, a longtime advocate of eating a plant-based diet. But his phrasing here surprises me. He seems to be suggesting that high protein in and of itself is bad, even if you’re getting your protein from low-calorie, low-fat sources like salmon.
Processed meats are so tightly linked to diabetes that we can inject rats with a compound from meat and cause diabetes. However, this is just processed meats we’re talking about. If you just cut some raw meat and then cook it, you’re mostly fine.
It should be made clear that the research appears reputable. The research does not rely upon statistical analysis that can be potentially biased. It’s about the presence or absence of genetic mutations in different species, making the results extremely robust. However, in this study the high Neu5Gc diet was 0.25 mg of Neu5Gc per gram of food. For comparison their estimated range of Neu5Gc content in beef is 0.023-0.231 mg per gram. Effectively the mice were fed ~1,000 times more Neu5Gc in their food than what is found in a steak. And the mice could only eat this pellet, whereas humans don’t only eat steak.
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 tumours. 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.
Red meat contains Neu5Gc. Pork has more Neu5Gc than beef, and dairy has it too. Fish contains trace amounts, and poultry has none. Cooking didn’t have a significant effect on the Neu5Gc content – cooking reduced water weight, and therefore increased the µg/g value. Here’s the chart from the paper:
Neu5Gc Content and Percentage of Various Food Groups
When our ancestors evolutionary diverged from chimpanzees, we developed a mutation in an enzyme known as CMAH. CMAH catalyzes the addition of a hydroxyl group to sialic acid (NeuNAc) to produce Neu5Gc (NeuNAc w/ added -OH). One of the things that makes you uniquely human compared to almost all other mammals are the patterns of carbohydrates that cover the surface of your cells. What makes you uniquely human is the striking lack of Neu5Gc on your cells compared to almost all other mammals.
Mutation of the CMAH enzymatic pathway may have promoted developmental brain complexity. This supports the view that human ancestors ate a primarily vegan diet. With little rare meat consumption to result in accelerated aging, the effects of this reduced fitness was outweighed by increased brain complexity that may have provided a survival advantage for mutants.
Glycoscience is a new branch of science that will help us get closer to understanding the human body in the finest details. If this research is confirmed to be true, it will have great implications on how to make consumption of red meat safe (genetic modification?) and could shed more light on how the body prevents cancer from spreading out of control (not everyone dies from cancer).