Scientist Finally Discover Why Eating Red Meat Causes Cancer

A new study out of the University of California, San Diego has discovered the culprit behind why eating red meat leads to higher instances of cancer -and it all has to do with a sugar.

Humans are the only animals that have a higher risk of cancer when it comes to eating red meat, as other carnivores eat red meat naturally with no ill side effects. The study, which was published December 29 in the “Proceedings of the National Academy of Sciences,” discovered that a unique sugar named Neu5Gc, found in most mammals but not in humans, triggers an immune response that in turn causes inflammation.

Ajit Varki, who led the study, explained the effect Neu5Gc had in mice: “Until now, all of our evidence linking Neu5Gc to cancer was circumstantial or indirectly predicted from somewhat artificial experimental setups … 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.”

This particular sugar can be found in red meats (using the nutritional definition of red meat, which includes pork and other livestock), cow’s milk and certain cheeses. Unfortunately for humans, our bodies can’t produce this sugar naturally, so when it is absorbed into our tissues, it is seen as a foreign invader. This then leads to the activation of our immune systems.

The result is inflammation.

And, while inflammation is not a great thing, in and of itself, it gets worse. If the immune system is subject to Neu5GC frequently, chronic inflammation will result. This inflammation can then lead to cancer. Those who regularly consume red meat will definitely suffer a stronger reaction than those who ingest red meat on an occasional basis.

Other animals, strict carnivores, who can make the Neu5GC sugar can eat red meats. Humans, not being strict carnivores, can’t. Therefore it seems clear that humans must avoid red meat consumption or face inflammation and possible cancer. At the minimum, reducing red meat ingestion will boost health.

A fourth study asked why people like red meat, and whether they were interested in eating less to improve their health. If Americans were highly motivated by even modest heath hazards, then it might be worth continuing to advise them to eat less red meat.

But the conclusion? The evidence even for this is weak, but the researchers found that “omnivores are attached to meat and are unwilling to change this behavior when faced with potentially undesirable health effects.”

Taken together, the analyses raise questions about the longstanding dietary guidelines urging people to eat less red meat, experts said.

“The guidelines are based on papers that presumably say there is evidence for what they say, and there isn’t,” said Dr. Dennis Bier, director of the Children’s Nutrition Research Center at Baylor College of Medicine in Houston and past editor of the American Journal of Clinical Nutrition.

David Allison, dean of the Indiana University School of Public Health—Bloomington, cited “a difference between a decision to act and making a scientific conclusion.”

It is one thing for an individual to believe eating less red meat and processed meat will improve health. But he said, “if you want to say the evidence shows that eating red meat or processed meats has these effects, that’s more objective,” adding “the evidence does not support it.”

Dr. Allison, who was not involved in the study, has received research funding from the National Cattlemen’s Beef Association, a lobbying group for meat producers.

The new studies were met with indignation by nutrition researchers who have long said that red meat and processed meats contribute to the risk of heart disease and cancer.

“Irresponsible and unethical,” said Dr. Hu, of Harvard, in a commentary published online with his colleagues. Studies of red meat as a health hazard may have been problematic, he said, but the consistency of the conclusions over years gives them credibility.

Nutrition studies, he added, should not be held to the same rigid standards as studies of experimental drugs.

Evidence of red meat’s hazards still persuaded the American Cancer Society, said Marjorie McCullough, a senior scientific director of the group.

“It is important to recognize that this group reviewed the evidence and found the same risk from red and processed meat as have other experts,” she said in a statement. “So they’re not saying meat is less risky; they’re saying the risk that everyone agrees on is acceptable for individuals.”

At the heart of the debate is a dispute over nutritional research itself, and whether it’s possible to ascertain the effects of just one component of the diet. The gold standard for medical evidence is the randomized clinical trial, in which one group of participants is assigned one drug or diet, and another is assigned a different intervention or a placebo.

But asking people to stick to a diet assigned by a flip of a coin, and to stay with it long enough to know if it affects the risk for heart attack or cancer, is nearly impossible.

The alternative is an observational study: Investigators ask people what they eat and look for links to health. But it can be hard to know what people really are eating, and people who eat a lot of meat are different in many other ways from those who eat little or none.

“Do individuals who habitually consume burgers for lunch typically also consume fries and a Coke, rather than yogurt or a salad and a piece of fruit?” asked Alice Lichtenstein, a nutritionist at Tufts University. “I don’t think an evidence-based position can be taken unless we know and adjust for the replacement food.”

The findings are a time to reconsider how nutritional research is done in the country, some researchers said, and whether the results really help to inform an individual’s decisions.

“I would not run any more observational studies,” said Dr. John Ioannidis, a Stanford professor who studies health research and policy. “We have had enough of them. It is extremely unlikely that we are missing a large signal,” referring to a large effect of any particular dietary change on health.

Despite flaws in the evidence, health officials still must give advice and offer guidelines, said Dr. Meir Stampfer, also of the Harvard T.H. Chan School of Public Health. He believes that the data in favor of eating less meat, although imperfect, indicate there are likely to be health benefits.

One way to give advice would be to say “reduce your red meat intake,” Dr. Stampfer said. But then, “People would say, ‘Well, what does that mean?’”

Officials making recommendations feel they have to suggest a number of servings. Yet when they do, “that gives it an aura of having greater accuracy than exists,” he added.

Questions of personal health do not even begin to address the environmental degradation caused worldwide by intensive meat production. Meat and dairy are big contributors to climate change, with livestock production accounting for about 14.5 percent of the greenhouse gases that humans emit worldwide each year.

Beef in particular tends to have an outsized climate footprint, partly because of all the land needed to raise cattle and grow feed, and partly because cows belch up methane, a potent greenhouse gas.

Researchers have estimated that, on average, beef has about five times the climate impact of chicken or pork, per gram of protein. Plant-based foods tend to have an even smaller impact.

Perhaps there is no way to make policies that can be conveyed to the public and simultaneously communicate the breadth of scientific evidence concerning diet.

Or maybe, said Dr. Bier, policymakers should try something more straightforward: “When you don’t have the highest-quality evidence, the correct conclusion is ‘maybe.’”

If for some reason you believe eating red meat every day (even if it is grass-fed) isn’t a bad thing, well now you have proof. Sorry, meat eaters, humans just aren’t built to be true carnivores.

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