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- Two newly published studies have suggested a link between vegetarianism and depression.
- The one study focused on a Brazilian population while the other involved a large group of Britons.
- However, both studies have limitations worth noting and further research is needed before firm conclusions can be drawn.
Two recent studies have suggested a link between meatless diets and depression, but some experts believe more in-depth research is required to confirm these findings.
The one study, published this month in the Journal of Affective Disorders, found that vegetarians experienced depressive episodes twice as often as those who ate meat. The findings were based on a survey that analysed the responses from just over 14 200 people between the ages of 35 and 74 in Brazil.
A questionnaire was used to determine whether people followed a meatless diet, while a diagnostic tool, called the Clinical Interview Schedule-Revised (CIS-R), was used to determine whether people had episodes of depression.
The link, the researchers wrote, was independent of socioeconomic factors and lifestyle factors such as physical activity, smoking, drinking alcohol and body mass index (BMI). The exact reason for these findings is unclear.
READ MORE | The 7 types of vegetarian diets from lacto-ovo to vegan, explained by a nutritionist
“Depressive episodes are more prevalent in individuals who do not eat meat … The nature of the association remains unclear, and longitudinal data are needed to clarify causal relationship,” they wrote.
The authors hypothesised the link may be partly due to nutrient deficiency, as earlier research has shown it to be the most common cause of a depressed immune system.
For example, the researchers of a 2020 study noted that “the health of the immune system is greatly affected by a person’s nutritional status.” Certain foods, including excess consumption of sugar and allergenic foods, can depress immune function, they said, while dietary factors that enhance immune function include all essential nutrients, antioxidants, carotenes, and flavonoids.
But in the recent study, the team did not find this association.
The second study
In another study, also published recently and in the Journal of Affective Disorders, researchers found that “beef intake may causally lower the risk of major depression”.
The study included the health data of more than 440 000 people in the UK, 45 000 of whom had depression. Beef was the only food linked to a lower risk of depression.
The team of psychiatrists, from the National Taiwan University, the Massachusetts General Hospital, and other centres, said that how beef could be protective against depression is not exactly clear, but suggested that nutrients found in beef, including protein, iron, zinc, and B vitamins, are known to help brain functioning and may be behind the protective effect.
READ MORE | Study suggests ultra-processed food can affect our brain health
However, they also noted that “potential mechanisms need to be further investigated to support our novel findings.”
But Harvard University researchers in 2017 reported that “a dietary pattern characterised by a high intake of fruit, vegetables, whole grain, fish, olive oil, low-fat dairy and antioxidants and low intakes of animal foods was apparently associated with a decreased risk of depression.”
A diet that is high in red or processed meat, refined grains, sweets, high-fat dairy products, butter, potatoes and high-fat gravy, and a low intake of fruits and vegetables, however, was associated with an increased risk of depression, they added.
Experts disagree
The latest research has led to some experts questioning the findings and methodologies.
Mary Mosquera-Cochran, registered dietitian at the Ohio State University Wexner Medical Center, told Healthline that since the researchers of the Brazilian study analysed the data, rather than conduct a controlled experiment, it’s hard to firmly say that a vegetarian diet causes depression.
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“The researchers found that diet quality was somewhat associated with higher rates of depression, but it did not fully explain the association,” said Cochran, who was not involved in the study.
She further highlighted that the same study sample had a very small percentage of people that were actually vegetarians — just 82 people out of about 14 200 people.
“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.
READ MORE | Ultra-processed foods are trashing our health – and the planet
While in this study the team found no link between nutrient deficiencies and depression, another expert told Healthline that it was certainly possible.
“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,” said Monique Richard, spokesperson of the Academy of Nutrition and Dietetics. She explained that it was important to delve deeper into the dietary patterns of these individuals to confidently exclude nutrient deficiencies.
“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.”
