Why Did Media Outlets Try to Convince Us That Vegetarianism Causes Cancer? Here's the Diet That Can

Different diets work for different people. That's one of the primary takeaways from a fascinating new study from Cornell University, which showed how human genetics customize to specific diets over generations, optimizing the body for the metabolism of certain foods.


Unfortunately, that message didn’t reach as many people as it could have, thanks to the way many media outlets handled it.

A Vegetarian Diet Might not be as Healthy as you Think,” ran one headline. “Being Vegetarian Could Kill You, Science Warns” screeched another.

Meat lovers rejoiced. Animal lovers panicked. The researchers who conducted the study wondered how a press release titled “Eating Green Could Be in Your Genes,” which was given to the media days ahead of its official release, could have gotten the story so wrong.

After the initial flareup and predictable backlash, most responses to the study were either “OMG vegetarian diet causes cancer,” or “OMG that is so much BS.” Very little coverage explored what this research actually revealed or what it might mean.

Published in the journal Molecular Biology and Evolution, the paper compares the DNA of people who come from vegetarian societies with the DNA of those from non-vegetarian, primarily meat-eating societies. They were specifically interested in a certain gene, called FADS2, and its mutant or variant forms.

When a gene has several forms (like, say, a gene for hair color), the many versions are called alleles. In this case, the gene controls how fats are digested. Different genes code for better digestion of animal fats, while others are more optimized for plant fats.

The FADS2 gene, and its plant- and meat-friendly alleles, help the body process the omega-6 and omega-3 fatty acids we consume from dietary sources. We need both of these oils, and it is becoming increasingly clear that the two fats should be present in the body in roughly equal parts. Omega-3 is anti-inflammatory, while omega-6 is pro-inflammatory. Inflammation is key to the body’s defense mechanisms, but too much or chronic inflammation can help cause many types of disease.

The “vegetarian allele” helps people regulate their bodies’ balance of omega-3 and omega-6 oils when the precursors are consumed specifically from plant-based sources. The researchers found that the plant-optimized alleles were most common in vegetarian societies, such as India.

They also suspected that the vegetarian gene would be problematic among people who eat primarily meat, because omega-3 and 6 oils from animal products are metabolized differently. Indeed, the vegetarian allele is quite infrequent in Greenland (where people traditionally eat meat from marine mammals, game, birds and fish), and actually seems to have been deleted from genes where they once existed, generations ago.

This was never intended to be a referendum on the relative merits or dangers of a meat- vs. plant-based diet. It’s a neat little confirmation of evolutionary principles at work. And while they don’t make specific dietary recommendations, the authors do extrapolate that a diet appropriate for someone with meat-eating genes might not work for someone with the so-called vegetarian allele. And vice versa.

This is where the conversation somehow degenerated into the vegetarians vs. carnivores and cancer and heart disease. And the take-home message seemed to be lost on most: There is no one-size-fits-all ideal diet that works for everyone, in every place.

“Our genetic heritage, to some degree, tailors our genes to specific foods, and when that changes dramatically for whatever reason, there may be a mismatch,” explained the study’s lead author Tom Brenna of Cornell, in a recorded presentation his lab sent to me.

This mismatch between diet and genes is the underlying premise behind the concepts of precision medicine and precision nutrition, which, Brenna and his team believe, is the way of the future. “[Precision nutrition/medicine] means making recommendations on a person-by-person basis rather than on global means, which is what dietary guidelines do.”

All of the team members I reached out to expressed their frustration at the spinning of their work into the notion that “a vegetarian diet can kill you.” As co-author Alon Keinan explained, if a scary headline needs to be made, if anything they said the exact opposite.

“Where the media took the 'cancer' part is from the fact that people whose ancestors have been vegetarian (and hence, carry the vegetarian allele), are at risk of having too much omega-6 if they start also eating meat.”

He also pointed out that heart disease is more likely than cancer to arise from an imbalance between omega-6 and omega-3 fats.

Certain vegetable oils like sunflower, safflower and soy are rich sources of omega-6. The recent gain in popularity of these oils in the Western diet has helped skew the balance of omega-3 and omega-6 in many people. While the ideal ratio is 1:1, among those who consume a Western diet it is now as high as 15:1 in favor of omega-6.

This is just fine, according to the American Heart Association and other establishment groups, which have recently doubled down on their denial of the idea that too much omega-6 is a concern. But among researchers at the front lines, there is growing agreement regarding the importance of balance over absolute quantities of these oils. And the food industry, which once celebrated the health benefits of omega-6 oils, is now quietly breeding its oilseed plants toward omega-3 heavy profiles, Brenna explained.

“Sunflower oil used to be 75 percent omega-6,” he says. “Most of it now is high oleic [meaning high omega-3], and is about ten percent linoleic [aka high omega-6].”

Today’s industrially produced vegetable oils, in fact, have come to resemble olive oil, Brenna says, which is the “stereotypical high-oleic oil." The fact that other oils are transitioning to high-oleics is good, he believes. But this isn’t yet a worldwide trend, and developing countries are still using the high linoleic versions, he says. “I’m quite concerned about developing countries in this regard.”

In other words, those who have the vegetarian gene but consume a Western, fast-food-based diet are particularly at risk. This helps explain the skyrocketing levels of cancer and heart disease, not to mention diabetes, in India, where the people are consuming a diet that doesn’t suit their genes.

With so much nuance and diversity in finding someone’s ideal dietary requirements, Brenna says, “What I’m worried about is folks just focusing on vegetables vs. meat.”

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