According to a new study published this month in the Journal of Affective Disorders, vegetarians experienced depressive episodes twice as often as those who ate meat.
The Academy of Nutrition and Dietetics explains that vegetarianism is defined in various ways, with some people opting to still consume dairy and/or eggs. However, the common thread in all forms of vegetarianism is the avoidance of meat.
Vegans, on the other hand, do not eat any animal products at all, including honey.
There are many reasons that people choose to eat a meatless diet, including ethical considerations, concern for the environment, religious beliefs, and health benefits.
Investigating the link between meatless diets and depression
The survey looked at 14,216 people in Brazil between the ages of 35 to 74. A food frequency questionnaire was used to determine whether people followed a meatless diet.
A diagnostic tool called the Clinical Interview Schedule-Revised (CIS-R) was used to determine whether people had episodes of depression.
The researchers found, upon analysis of the data, that meatless diets were associated with twice the frequency of depressive episodes. Further, this association was independent of socioeconomic factors as well as lifestyle factors like smoking, alcohol intake, physical activity levels, and body mass index (BMI). The exact reason for these findings is unclear.
Mary Mosquera-Cochran, a registered dietitian at The Ohio State University Wexner Medical Center who was not a part of the study, said that due to the way the study was designed — analyzing data rather than conducting a controlled experiment — it can’t be concluded whether a meatless diet actually does cause depression.
“The researchers found that diet quality was somewhat associated with higher rates of depression, but it did not fully explain the association,” said Cochran.
She further explained that the researchers hypothesized that this link might exist because people who are depressed are more likely to try dietary changes (like cutting out meat, for example) because they are hoping to feel better.
Cochran said that the study was done on Brazilian citizens, so it also may not apply to other populations.
She additionally pointed out the fact that it was only a very small percentage of people in the sample studied were actually vegetarians — 82 people out of around 14,000 total.
“The authors note that it’s currently estimated that 5-14% of Brazilians currently follow a vegetarian style diet, so this sample may not be reflective of all vegetarians in Brazil either,” said Cochran.
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Why might meatless diets cause depression?
Though the authors also note that they adjusted for factors like protein and micronutrient intake, concluding that they believe “nutrient deficiencies do not explain this association,” other experts disagree.
Academy of Nutrition and Dietetics spokesperson Monique Richard, said meatless diets and depression could be linked for a variety of reasons, with one being nutrient deficiencies.
“Whenever an individual excludes an entire food group, in this case, protein and fat sources, and does not replace it with equally nutritionally-adequate options, it will affect a variety of systemic and physiological functions such as cognitive health,” she said, noting that it is important to look deeper into the dietary patterns of these individuals to learn whether this might have been the case.
“If an individual does not have an adequate intake of nutrients such as B12, omega-3 fatty acids, and protein, certain enzymes and proteins may be compromised, altering specific pathways in the body,” said Richard. “This could affect mood, anxiety, memory, perceived stress, sleep, etc.”
As an example, she cites the amino acid tryptophan, which is needed to make serotonin, an important neurotransmitter that has been linked to mood disorders like depression.
Tryptophan is found in meat as well as oats, nuts, and seeds, explained Richard. But it’s important that people are educated on what foods contain it and how to consume enough to meet their own personal needs.
“Other factors that would be important to assess would be if the person felt isolated or disconnected from others related to their dietary choice,” said Richard. “Is there a personal, religious, or moral consideration for the choice that may also be contributing to these feelings and state of mind?”
How to get adequate nutrition on a meatless diet
Dr. Mary-Jon Ludy, Chair of the Department of Public and Allied Health and Associate Professor of Food and Nutrition at Bowling Green State University, advised that “[w]ith or without meat, it is important to follow a healthy, high quality eating pattern that is rich in fruits, vegetables, whole grains, and lean protein.”
“Eating a variety of nutrient-dense foods as well as limiting added sugars, solid fats, and sodium is key,” she said.
According to Samantha Coogan, Program Director of the Didactic Program in Nutrition and Dietetics at the University of Nevada, Las Vegas, the main vitamins and minerals of concern when it comes to depression are the B vitamins, zinc, magnesium, and selenium.
Vitamin B12, in particular, is only found in animal products, said Coogan. However, it, along with other B complex vitamins, are responsible for mood regulation and brain function.
“B vitamins can be found in fortified breakfast cereals, and B12 in fish, eggs, meat, and milk products,” she said. Additionally, most people who don’t eat meat will need to take a B12 supplement.
She further notes that a B complex supplement may be a better option since you’ll get the amount of B12 that you need along with the other B vitamins.
“Zinc may play a role in endocrine pathways that may lead to increased levels of cortisol, and the regulation of neurotransmission as a potential mechanism of action, so a deficiency could disrupt usual neurotransmitter firing/signaling to other areas of the body, such as elevating the expression of the hippocampus and decreasing cortisol,” explained Coogan.
She noted that zinc is mainly found in red meat, crab, and oysters, making it difficult for a vegan or vegetarian to get enough. However, it can also be found in nuts, whole grains, fortified cereals, and dairy products.
Coogan further explained that magnesium is responsible for the activation of more than 300 enzyme systems that play important roles in brain function.
“Low magnesium can lead to inflammation, dysregulation of oxidative pathways possibly inducing oxidative stress, and may dysregulate the release of serotonin, dopamine, noradrenaline, and sleep cycles (i.e. interrupting sleep/insomnia),” she said.
But, when it comes to getting enough magnesium, plant eaters are in luck, according to Coogan. This important mineral is found mostly in plant-based foods, including leafy greens, legumes, nuts, seeds, and whole grains.
Lastly, selenium deficiency can cause thyroid dysfunction, inflammation, oxidative stress, and dysregulation of important mood regulators like serotonin, dopamine, and noradrenaline.
“Selenium is primarily found in seafood, poultry, meat, eggs, and fish,” said Coogan. However, it can also be found in bread and grains.
Ludy concluded by stating, “If in doubt, meeting with a registered dietitian nutritionist (RDN) can be a great resource for planning a well-balanced diet.”
The Academy of Nutrition and Dietetics maintains a database of RDNs on its website, or you can ask your primary care provider for a referral.