Vegan, vegetarian diets may increase susceptibility to depression

Following vegan and vegetarian diets, which offer plenty of what is good for health, has been reported to have a downside: an increased risk of depression and anxiety, especially for younger adults.

The finding may be explained by a reverse causal relationship, whereby individuals with psychosocial disorders are keener to follow the said diets to improve their mental health, according to the investigators.

“Other possible explanations from the literature include nutrient deficiencies common in vegan diets (eg, certain amino acids, long-chain omega-3 fatty acids, vitamins B6 and B12, zinc, creatine, and even cholesterol) that could accelerate or worsen pre-existing mental conditions. All these deficiencies have been linked to a higher risk of mental health disorders,” they added. [Am J Clin Nutr 2009;89:1627S-1633S; Indian J Psychiatry 2008;50:77-82; Psychother Psychosom 2004;73:340-343]

The investigators performed a meta-analysis of 13 studies evaluating the effect of vegetarian (lacto-ovovegetarian, ovo-vegetarian, or lacto-vegetarian) or vegan diets on mental or cognitive outcomes in 17,809 adults in total. Most studies were of medium quality.

Pooled data showed that relative to an omnivorous diet, vegan and vegetarian diets were associated with an elevated risk of depression (odds ratio, 2.142, 95 percent confidence interval [CI], 1.105–4.148; I², 65.4 percent; p=0.089) but lower levels of anxiety (mean difference [MD], −0.847, 95 percent CI, −1.677 to −0.018; I², 92.08 percent; p=0.001). There was no effect seen on stress and memory impairment. [Nutr Rev 2020;doi:10.1093/nutrit/nuaa030]

Clear age-dependent patterns emerged in subgroup analyses, such that vegans and vegetarians aged <26 years were at higher risk of the following mental health outcomes than younger omnivores: depression (MD, 1.739, 95 percent CI, 0.758–2.719), anxiety (MD, 0.901, 95 percent CI, 0.143–1.658), and stress (MD, 1.033, 95 percent CI, 0.478–1.587).

“[The above finding] might reflect the greater vulnerability of young people to nutritional deficiencies, since their brain and personality are still developing,” the investigators noted.

In the present study, vegetarians and lacto-ovovegetarians were described as those who abstained from eating meat, fish, and seafood but not milk and dairy products from their diet. Vegans, on the other hand, were defined as those who excluded any kind of animal product from their diet.

“The necessary intakes of protein, fat, carbohydrate, vitamins, and minerals within vegetarian and vegan diets for optimal health is still under investigation. [Individuals who follow such diets] may require supplementation, as some nutrients may not be adequately available from plant sources,” according to the investigators.

“Some supplements (eg, vitamin B12, zinc, and creatine) to improve short-term memory and intelligence/reasoning may help in very restricted diets. Otherwise, a well-chosen plant-based diet provides all the necessary protein, fats, carbohydrates, vitamins, and minerals for optimal health,” they said.

While the present meta-analysis highlights the potential for negative mental health outcomes in individuals who adopt a vegetarian/vegan diet, the considerable heterogeneity among the included studies prevents definitive conclusions from being drawn, as the investigators pointed out. “A major flaw in current literature on this topic is the lack of adjustment for confounders.

“More studies on the effects of vegan or vegetarian diets on mental health, especially cognitive outcomes, with overall better quality are needed before clear positive or negative associations can be confirmed,” they added.