Bad Science Reporting: Vegetarian Diets DON’T Cause Cancer

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The Independent has just published an article with the headline, “Vegetarians are ‘less healthy and have a lower quality of life than meat-eaters’, scientists say” and the subheading, “Controversial study suggests non-meat eaters are more at risk of physical and mental illness, despite leading healthier lifestyles.” Yikes! I’m a vegetarian-leaning person so this was of great interest to me.

First let me lay my cards on the table. I’ve been vegetarian or vegetarian-adjacent for about 20 years now, and by “vegetarian-adjacent” I mean that about a decade ago I went from vegetarian to pescetarian, which means I occasionally eat seafood. My reasons for my diet are varied. For a start, I think it’s stupid that anyone should have to validate any generally healthy diet. Among the people who have asked me to validate my own choices, a very small percentage have ever considered the reasons why they eat what they do. Their actual reasoning, if explored, would most likely be something along the lines of “because that’s what I grew up eating and it’s what society tells me to eat.” The fact that I’ve thought about what I eat shouldn’t force me to be on the defensive when I turn down a hamburger at a barbecue.

That said, I will briefly tell you my reasons: for one, I generally like animals when they’re alive and I don’t like being the direct cause of their deaths if I don’t have to be. If I am going to be the cause, I want the animal to be as intellectually as close to a vegetable as possible and also to know that I could do the killing if I needed to, both of which apply to fish. Two, research shows that reducing the amount of meat humans eat would go a long way towards helping the environment in many ways (despite over-the-top headlines that misrepresent the science). And as a distant third reason, yes, research shows that eating less meat is healthier. I say that one is a distant third because come on, Oreos are vegan. I’m not exactly a health nut.

But it’s true: research by and large shows that vegetarian diets are healthier than meaty diets, though vegans have to be careful to get all the nutrients they need through supplements and careful diet planning. So the study described in the Independent contradicts the previous body of research, which means that it’s helpful to turn a very critical eye to it.

The study itself looked at 1,320 Austrians split according to their diet: vegetarian, meat-eater with lots of fruits and vegetables, meat-eater who reduces the amount of meat they eat, and meat-rich meat-eater. Already you may notice a problem: there are four groups, only one of which is vegetarian. When you combine this with the fact that the researchers weren’t looking at just one health parameter but instead at dozens of different issues, this makes it extremely likely that any one of the other three groups may score “healthier” than the vegetarian group with any one vector.

You should always be skeptical of research that does this scatter-shot approach — it doesn’t mean the study is useless, but it does mean that you’re much more likely to get false positives when you’re looking for absolutely anything that seems out of place in the data. It’s really obvious when you look at the charts in the paper, which list dozens of possible conditions and highlighted the handful that the vegetarian group scored higher on. That’s why research like this is more often just preliminary, and more rigorous studies can follow-up on investigating what it turns up.

So the researchers did find that the vegetarian group showed a very slight increase in rates of cancer, allergies, and mental health issues like anxiety and depression. How slight, you ask? I’m glad you asked, by the way, because the Independent doesn’t even mention that it’s slight. The vegetarian group had a 4.8% difference in cancer rates, compared to 3.3% for meat-eaters who eat vegetables. They had a starker difference in mental illness: 9.4% compared to 4.5 to 5.8% for the various groups of meat-eaters. Ditto allergies: 30.6% compared to 16.7 to 20.3% among the meat-eaters.

That said, there is a statistically significant difference. Does that mean going vegetarian will increase your rate of cancer, mental illness, and allergies?

No. Absolutely not. For a start, this could still be a statistical anomaly that disappears once a follow-up study can drill down on those exact conditions. We’re talking about 300 people in each group, and again, the researchers were looking for literally any increase in any type of condition.

But setting that aside, even the researchers argue that the Independent’s headline is wrong: “we cannot say what is the cause and what is the effect.” In other words, this shows possible correlation, not causation. People who get cancer may be more likely to switch to a vegetarian diet in order to be healthier. People with allergies may be more likely to think critically about what they’re eating and follow a more restrictive diet because the stakes are higher for them. Anxiety may make you more likely to follow a restrictive diet. Or psychiatrists may encourage depressed patients to change their diet in order to feel better.

I could go on but I think you get my point: the researchers are very clear that no where in their work does the data even imply that vegetarian diets are less healthy than meaty diets. And what’s incredible is that the Independent quoted them on that and then ran that quote under a false headline anyway. I know I can’t expect better from mainstream science reporting, but man is it frustrating to know that vegetarians everywhere will have an uptick in “concerned” family and friends shoving this article in their faces when they’re inevitably forced to validate their dietary choices.

Rebecca Watson

Rebecca is a writer, speaker, YouTube personality, and unrepentant science nerd. In addition to founding and continuing to run Skepchick, she hosts Quiz-o-Tron, a monthly science-themed quiz show and podcast that pits comedians against nerds. There is an asteroid named in her honor. Twitter @rebeccawatson Mastodon Instagram @actuallyrebeccawatson TikTok @actuallyrebeccawatson YouTube @rebeccawatson BlueSky

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