Vegetarians who eat more processed foods are at higher risk of developing depression

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Not all vegan and vegetarian diets are healthy – and one consequence of a low-quality plant-based diet could be poorer mental health.

New research has found plant-eaters with a taste for processed foods are more susceptible to depression than peers with diets high in fresh produce.

Megan Lee, a researcher in nutritional psychiatry at Bond University, said the findings were significant given the increasing popularity of vegan and vegetarian lifestyles and the proliferation of packaged foods targeting those markets.

Many of the products are high in refined vegetable oils and refined grains, salt and sugar, she said.

“There is a general perception that following a plant-based diet is inherently healthy but like any diet it comes down to what you put in your mouth,” said Dr. Lee, the lead author of the study.

“Vegans and vegetarians are not automatically eating heaps of fruit and veg because there are all these products out there that are fully processed, fully refined.

“People may inadvertently be consuming high levels of processed plant foods which is a known risk factor for increased depression.”

For the study, researchers examined the diet quality and mental health of 219 vegans and vegetarians in Australia.

The participants were asked to complete questionnaires based on recognized measures of diet quality and depression.

Those with diets high in fresh fruit, vegetables, nuts, seeds, legumes and whole grains were found to be at lower risk of depression compared to fellow vegans and vegetarians with low quality diets.

Dr. Lee said the protective effect of a high-quality plant-based diet was likely due to the presence of complex carbohydrates, fiber, probiotics and antioxidants which have all been found to decrease symptoms of depression.

But she said the research indicated switching to a high-quality plant-based diet was not a “cure” for those already experiencing depression.

“It seems to have more a protective role,” she said. “Our research did not find that a plant-based diet was a treatment or fix for those who were already depressed.”

Vegans and vegetarians are already more vulnerable to depression than the general population.

Dr. Lee said this could be due to their outlook on life and that they are generally a younger cohort which is already more susceptible to mental health issues.

“We think this (susceptibility to depression) might be because vegans and vegetarians tend to be more conscious about external issues – animal welfare, environmental concerns – and they can be ostracized socially because of their choice of diet.”

Participants in the study were aged 18 – 44 which closely corresponds with the 15 – 44 age group for which suicide is the leading cause of death in Australia. Almost 14 percent of people in this age group report experiencing symptoms of depression.

The research also holds good news for meat-eaters looking to protect their mental health.

“Even if we are meat-eaters we can still benefit from preventive and protective food by consuming more fruits and vegetables,” Dr. Lee said.

More than 2.5 million Australians have chosen to go meat-free – about 12 percent of the total population.


Over 300 million people globally experience symptoms of depression.1 Mood disorders, including depression, are significant predictors of suicide and suicidal ideation and are responsible for over 800 000 global suicide-related deaths per year.1 In Australia, 1 in 10 people (10.4%) report experiencing symptoms of depression. In younger adults, the prevalence rate of depression is higher at 13.9%, with suicide the leading cause of death for individuals aged 15–44.2

The most common treatments for depression are pharmacology and psychotherapy. However, approximately one-third of patients do not respond to conventional treatments and can develop treatment-resistant depression.3 Increasingly, lifestyle changes such as diet and exercise have been shown to impact symptoms of depression positively and could be both a cost-effective and modifiable adjunct treatment to current traditional treatment options.4

Both poor diet and mood disorders are known leading causes of morbidity and mortality.5 6 Diet quality is ‘The nutritional adequacy of an individual’s dietary pattern and how closely this aligns with (Australian) national dietary guidelines’.7 However, there is confusion surrounding the term ‘diet quality’ with minimal agreement on a valid diet quality measurement.8

Dietary patterns include the variety and quality of foods and beverages in a diet and the quantity and frequency they are habitually consumed.9 Dietary patterns are most often evaluated based on their inclusion or exclusion of healthy and unhealthy foods and beverages. Healthy dietary patterns, including traditional and Mediterranean diets, are loosely defined as a healthy intake of fresh fruit, vegetables, nuts, seeds, legumes, whole grains, water, lean meats and dairy.10 11

Plant-based dietary patterns are commonly divided into two main categories, vegan and vegetarian, with several subcategories low in animal food consumption.12 As such, a healthy plant-based dietary pattern is characterised by high consumption of fresh fruit, vegetables, nuts, seeds, legumes, whole grains and water, but may omit lean meats and dairy.13 14

Conversely, unhealthy dietary patterns are characteristic of a large consumption of ultraprocessed, refined and sugary foods, despite the inclusion or exclusion of animal-based products.15–18 In Australia, there has been a surge of people choosing to follow plant-based lifestyles with over 2.5 million Australians choosing to go meat-free. This equates to 12% of the total population, with the largest proportion of plant-based dieters being young adults between 18 and 45.19

Dietary intervention studies highlight healthy dietary patterns rich in fresh fruits, vegetables, nuts, seeds, whole grains and legumes as promising in reducing symptoms of depression.4 20 However, the evidence of the association between plant-based dietary patterns and depression is inconsistent and conflicting.21 Some studies suggest that plant-based diets (PBD) are associated with improved mood and mental health.22

Others suggest that PBDs are associated with a greater risk of depressive symptoms,23 24 while others find no relationship.25–27 A meta-analysis of 13 studies by Iguacel et al 28 found that vegans and vegetarians were at increased risk of depression (OR=2.14, 95% CI: 1.11 to 4.15). Another systematic review and meta-analysis of ten observational studies by Askari et al 29 found no association between those who consumed a vegetarian diet and depression symptoms (pooled effect size: 1.02, 95% CI: 0.84 to 1.25).

While a narrative review of 19 studies by Jain et al.30 found conflicting information, some studies suggesting that those who adhered to vegan and vegetarian dietary patterns had higher depression rates, while others indicated they were associated with decreased depressive symptoms. Other primary research studies suggest that young adult vegetarians are at higher risk of depression31 and suicide32 than omnivores in the same age group.

The reasons for these conflicting findings are not yet fully understood but may be due to the lack of heterogeneity of the measurement of dietary patterns (self-report), and that quality rather than dietary patterns needs to be further explored in this population.33

Indeed a recent meta-analysis showed an increased risk of depression in vegetarians,34 however, the interpretation of the findings is limited due to the lack of methodological clarity in vegetarian diets being of ‘low’ or ‘no’ meat consumption. As such, diet quality measures in PBD is critical for exploring the association between diet and mental health.

This study explores the association between vegan and vegetarian dietary patterns and depressive symptoms in adults by exploring the overall dietary quality of these patterns. The research hypothesises that a high-quality PBD is associated with a lower risk of depressive symptoms.

reference link : https://nutrition.bmj.com/content/early/2021/10/28/bmjnph-2021-000332


Original Research: Open access.
“Plant-based dietary quality and depressive symptoms in Australian vegans and vegetarians: a cross-sectional study” by Megan Frances Lee et al. BMJ Nutrition, Prevention & Health

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