Can a vegetarian diet cause depression?

It looks that way. Here are three key brain nutrients to supplement on a meat-free diet

A study published in October 2021 found that a meat-free diet “was associated with poorer psychological health.” This systematic review of 18 studies of meat and mental health involved a total of over 160,000 participants. It concluded that:

“The most rigorous studies demonstrated that the prevalence or risk of depression and/or anxiety were significantly greater in participants who avoided meat consumption.”

This review may be highly significant, but it does not prove that a vegetarian diet causes mental health problems. It just highlights a strong relationship between two factors. Association is not causation, after all.

One irrefutable fact is that the food you eat can affect the way you feel. No surprises there: the brain is made of fat, protein, cholesterol and water, and is powered by a broad spectrum of micronutrients. Many of those nutrients are unique to animal-source foods — they are either missing from a plant-based diet or have low bioavailability, meaning they are poorly absorbed.

Therefore, there are potential risks involved in meat avoidance, including the development of depression and anxiety. Anyone who chooses a vegetarian diet needs to be aware of this and take the appropriate supplements. The important thing is to recognise the signs and symptoms of deficiency and know which supplements to take. Here are some of the key nutrients likely to be missing on a meat-free diet.

Vitamin B12

This vitamin is essential for the central nervous system and is found only in animal-source foods. Because the liver stores large amounts, deficiency symptoms can take a few years to appear. Mental symptoms include depression and anxiety, but there may also be fatigue, pallor, and hair loss. As liver storage starts to run out, you can also expect tingling or numbness of the hands and feet.

“In clinical studies, lower vitamin B12 levels have been found to be associated with severe depression. Low serum vitamin B12 levels are also detected in approximately 20% of psychiatric patients.”

Without supplementation, vitamin B12 deficiency can also lead to memory problems, dementia, and in rare cases psychosis. There may also be neurological issues, mainly myelopathy, where myelin sheaths and axons are destroyed in the white matter of the spinal cord. The myelin is the protective layer wrapped around the nerve. If detected in time, the condition is fully reversible. If not, the damage becomes permanent.

“Vegetarians have vitamin B12 deficiency and are more prone to developing neuropsychiatric and neurological problems.”

Vegetarians and vegans are vulnerable, but they are not alone: low vitamin B12 status can also arise from gastrointestinal conditions, including Crohn’s disease and gastric atrophy.

Pernicious anaemia is another causative factor in B12 deficiency. So too are smoking and certain medications, especially Metformin and antacids. Metformin, the drug commonly used to treat type 2 diabetes, lowers vitamin B12 levels in 30% of people who take this drug over a long period of time. Even so, low vitamin B12 is better than no vitamin B12.

Iron

Iron is the most abundant metal in the body, and the second most concentrated metal in the brain, after zinc.

Iron deficiency signs and symptoms include pallor, fatigue, headache, hair loss, brain fog, anxiety, and depression. In older people, there may also be cognitive decline.

There are two forms of dietary iron: heme and non-heme. Heme iron is found only in animal-source foods and has a higher absorption rate than non-heme iron. The human gut can absorb 25%-30% of heme iron from animal-source foods. That’s quite a good return: giving back is part of the circular nature of nourishment.

Non-heme iron is found in both animal and plant foods, especially leafy green vegetables. Plants contain only non-heme iron.

There is plenty of iron in plant foods, but it has very low bioavailability. Non-heme iron absorption can be as low as 2%. Studies of vegetarians in Australia, Canada, China, England, Germany, Korea, New Zealand, South Africa and the United States have found vegetarians, particularly vegetarian women, to have a high prevalence of iron depletion.

Menstrual loss and pregnancy put women at further risk of developing iron deficiency. Women who lack iron in pregnancy are more likely to have babies with neurocognitive deficits. Approximately 45% of women start their pregnancy with low or absent stores of iron, even though iron requirements increase ten-fold in the first trimester.

In the UK, approximately 46% of women develop anaemia at some point during pregnancy.

Zinc

Zinc is a trace element that plays an essential role in just about every function of the body, including cognitive function. It is highly concentrated in the brain and found mainly in the hippocampus and amygdala regions. The hippocampus — the most important area of the brain for memory, learning and neurogenesis — is the region most responsive to zinc status.

The best sources of zinc are seafood (especially shellfish), red meat (especially offal), poultry, and eggs. Zinc is also present in plant foods, including wholegrains, plants and seeds, but in much smaller amounts and in a much less absorbable form.

The body cannot store zinc in the long term, so a constant dietary supply is required. Intake and serum concentrations of zinc have been shown to be lower in people following vegetarian diets, compared with non-vegetarian people.

There has been a considerable amount of research into the association between zinc deficiency and depression, and most of this research suggests that the association is strong. In some cases, a correlation between severity of zinc deficiency and severity of depression has been demonstrated.

Various researchers have pointed out that depression can be reversed through dietary changes and/or supplementation with zinc. Indeed, supplementing with zinc as an adjunct to antidepressant drug treatment in patients with clinical depression has been shown to be significantly more effective than drug treatment with placebo.

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These three nutrients are arguably the most researched, in terms of depression and/or anxiety, and should be supplemented by anyone following a plant-based diet.

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A vegetarian diet per se does not cause depression , but the evidence suggests that it is the absence of crucial nutrients found mainly or exclusively within animal-source foods that can and does. If you choose a meat-free diet, be sure to take the appropriate supplements.

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