There are serious problems with a widely-shared study that claimed meat-eaters have better mental health than vegetarians
- A recent study of research on diet and mental health found a possible association between meat-free diets and risk of depression and anxiety.
- The data does not prove any causal link between meat eating and mental health, according to the researchers, despite some media headlines that the study found meat can improve mental health.
- The research itself was also funded by the beef industry, leading some experts to question its credibility.
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A new, polarizing study of diet and mental health suggests there may be a link between eating meat and psychological wellbeing.
Previous research shows an association between vegetarianism and a higher risk of depression and anxiety, according to the study, a systemic review of 18 other studies on meat consumption and mental health, published April 20 in Critical Reviews of Food Science and Nutrition.
A team of researchers from the Department of Psychology at the University of Southern Indiana found that 11 of the papers suggested meat eaters had better psychological health than vegetarians. Of the remaining 7 studies, three showed that vegetarians had better mood or mental health symptoms than meat eaters, and the other four had mixed results.
The researchers concluded that there is "clear evidence that meat-abstention is associated with higher rates or risk of depression, anxiety, and self-harm."
However, it's not so clear-cut.
Dr. Edward Archer, a co-author of the study and chief science officer for the data analytics firm Evoving FX, told Insider that the research does not show that meat can improve mental health, or that avoiding it can cause mental health issues.
"We were very careful to say no causal inference should be made. We offered lots of information for both sides of the debate," he said in an interview. "We cannot say that meat-free diets cause mental illness. What we did find is that the research doesn't support the idea that eliminating meat can improve mental health."
But that nuance got lost as the study was shared widely online.
The study didn't actually show that a meat-free diet causes depression or other mental health issues
Several media publications reported the research as showing that meat improves mental health outcomes.
Archer said that's not an accurate portrayal of the study.
"That's patently false, you can't make that statement. We did not claim that," he said.
Epidemiologist Gideon Meyerowitz-Katz noted on Twitter that the research shows that there may be a relationship between vegetarian and depression and/or anxiety, but it doesn't prove that eating a meat-free diet causes those issues.
In fact, one of the main studies included in the analysis found that some of the vegetarians had started a meat-free diet after being diagnosed with depression.
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Archer said there could be many factors to explain the link the study found between mental health and vegetarianism. A few possible explanations could that people try vegetarian diets to address existing health issues, or that people who are sensitive to ethical issues may be more likely to be both depressed and vegetarian.
"What we've shown clearly is that there's some relationship. There's a million ways of looking at this — individuals who are suffering from depression and anxiety will treat themselves with changes in dietary patterns," Archer said. "Or, individuals who are very sensitive to the suffering of others may take and ethical stance, and if you look at the amount of suffering, those people may become depressed and anxious because of that."
What the researchers actually conclude is that a vegetarian diet probably doesn't make depression or anxiety any better.
"Our study does not support meat avoidance as a strategy to benefit psychological health," the authors wrote.
An important take away, though, is that diet and psychological health are clearly related, according to Dr. Wendy Bazilian, a registered dietitian with a doctorate in public health. This kind of research can help us better understand that relationship, and make choices according to our unique circumstances and preferences, she said.
"I think there is some strength to what the study suggests that we need to look at that, whether you're a meat eater or not, maybe there isn't a one-size-fits-all," Bazilian told Insider. "I think some next steps are to make sure we're looking at nutrients that may be of concern to mental health, and checking in with mental health of our patients regardless of what diet they follow."
The study was funded by the beef industry
Meyerowitz-Katz also notes a glaring issue with the study: that it's funded by the meat industry.
The paper states it was "funded in part via an unrestricted research grant from the Beef Checkoff, through the National Cattlemen's Beef Association."
A Facebook post from the University of Southern Indiana notes that the study's lead author, assistant professor of psychology Urska Dobersek, received a $10,555 grant from the National Cattlemen's Beef Association "to conduct a systematic review on 'Beef for a Happier and Healthier Life.'"
Archer, who said he was not involved in that grant for the study, said the funding was primarily used to pay student researchers, and that it did not influence the design or analyse of the research. He added that all of the studies his team reviewed were funded by public health, not industry organizations.
"I think it's a legitimate point to look at the funders, but you have to make that next step to see if something was done wrong and if funders caused that," he said.
Bazilian agreed that it's not uncommon for industry funding to be involved in nutritional studies. While it's important to be aware of, it doesn't necessarily mean the research is flawed, particularly if the funding is transparent.
"Funding is a slippery slope and you definitely have to pay attention. Industries that have a vested interest want to know what the research says," she said. "It's important to important to know that and look beyond one study, even a review. I don't think that any one study is ever going to be the bottom line on a topic."
The authors say their study hammers home the limitations in nutritional research
The statistic, which led most of the media coverage, that "one in three vegetarians is depressed" is taken from just one of the studies in the analysis, a 1998-99 survey that included just a small percentage of vegetarians.
A small sample size can make the results of the study less certain. As the researchers noted in their report, the studies included in their analysis vary widely — in how they were conducted, how the conclusions were made, and how strong the evidence was to support those conclusions.
Archer has previously written extensively about the limits of nutritional research, and so cautioned against drawing hard conclusions about health based only on studies of diet.
"There are many other factors and components to health than what you eat," he said. Archer said that as a result, it's important to consider the information, but also take it (and other nutritional research) with a grain of salt.
"The things we can say are to eat a varied diet, enjoy it, exercise, and repeat daily, I think that's the most important point," he said.
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