Does a vegetarian diet help or harm your brain? Here’s what the science reveals

By Priyanjana Pramanik, MSc.Reviewed by Susha Cheriyedath, M.Sc.Mar 3 2025

While plant-based diets offer neuroprotective benefits, missing key nutrients like B12 and omega-3s could increase cognitive risks—learn how to optimize your diet for brain health.

Study: Impact of Vegan and Vegetarian Diets on Neurological Health: A Critical Review. Image Credit: Johnathan Ball / Shutterstock

In a recent review article in the journal Nutrients, researchers explored whether following vegetarian or vegan diets improves neurological health.

Their findings indicate that well-planned plant-based diets, rich in antioxidants and phytonutrients, can protect against oxidative stress and systemic inflammation, which contribute to neurodegeneration. However, care must be taken to support cognitive well-being while also preventing nutrient deficiencies, particularly in vitamin B12, omega-3 fatty acids, iron, zinc, selenium, and iodine, as these nutrients play crucial roles in brain function and neuroprotection.

Nutritional Differences Based on Diet

The global shift toward plant-based diets has been driven by ethical, environmental, and health considerations. These diets are associated with a lower risk of chronic diseases like cardiovascular disease, obesity, and type 2 diabetes. However, the impact of plant-based diets on neurological health remains underexplored.

Vegetarian and vegan diets differ in nutrient composition. Vegan diets lack key nutrients such as omega-3 fatty acids, vitamin B12, vitamin D, iodine, iron, zinc, selenium, and calcium.

Vitamin B12 deficiency is particularly concerning, with deficiency rates ranging from 11% to 90%, depending on supplementation, age, and dietary habits. This deficiency is linked to elevated homocysteine levels, a risk factor for Alzheimer’s and cognitive decline.

Similarly, iron deficiency affects up to 30% of vegans in Western countries and up to 60% in regions like South Asia, leading to cognitive impairment. Deficiencies in omega-3s (specifically DHA and EPA) and low iodine levels further impact brain health. Since the conversion rate of ALA (found in flaxseeds and walnuts) to DHA and EPA is below 10%, algae-based DHA/EPA supplementation is strongly recommended.

Vegetarians who consume eggs and dairy are less likely to experience such deficiencies while benefiting from a higher fiber intake and antioxidants. The high fiber content promotes beneficial gut microbiota, which produces short-chain fatty acids (SCFAs) such as butyrate, which supports brain health and reduces inflammation.

Neurological and Mental Health Benefits of Plant-Based Diets

Plant-based diets contain numerous bioactive compounds, including flavonoids, carotenoids, and polyphenols, which are critical for reducing inflammation and oxidative stress. These benefits are crucial for protecting against neurodegenerative diseases like Parkinson’s and Alzheimer’s.

These diets also have a neuroprotective effect by reducing systemic inflammation, which contributes to neurodegeneration and cognitive decline. Moreover, they support mood regulation by influencing serotonin production, thereby improving mental well-being. However, poorly planned diets may increase the probability of developing deficiencies that affect brain health and elevate the risk of depression, anxiety, and cognitive impairment.

Plant-based diets have been shown to influence mood and mental well-being. On the positive side, they are linked to improved mood, reduced anxiety, and enhanced happiness, particularly when combined with regular exercise. However, some research suggests that if deficiencies in B12, omega-3s, and iron persist, the risk of depression and cognitive decline may be significantly heightened.

Addressing Nutrient Deficiencies

To maximize the neurological benefits of plant-based diets, it is crucial to address potential nutrient deficiencies. Supplementation and dietary planning can help overcome the challenges of vitamin B12, iron, zinc, selenium, and omega-3 fatty acid deficiencies.

Vegan diets, in particular, need to ensure adequate intake of B12 through fortified foods or supplements. Similarly, vegetarians should ensure sufficient intake of omega-3s through sources like flaxseeds or algae-based supplements, which provide direct DHA and EPA, rather than relying on inefficient ALA conversion.

Biofortified foods—such as zinc-enriched rice, low-phytate wheat, and selenium-enhanced crops—are emerging as promising solutions to improve nutrient intake in plant-based diets. Public health initiatives should educate on these risks and implement targeted policies to improve access to fortified foods in low-resource settings.

Antinutrients and Bioavailability

Plant-based foods contain secondary metabolites, known as antinutrients, which interfere with the absorption of essential nutrients. Common antinutrients include phytates, oxalates, and lectins.

While antinutrients may pose risks by promoting oxidative stress and inflammation, they also have health benefits, such as antioxidant and anti-inflammatory properties. Proper food preparation techniques—such as soaking, sprouting, fermenting, and cooking—can significantly reduce the negative impact of antinutrients while preserving their beneficial properties.

Conclusions

Vegetarian and vegan diets offer significant neurological benefits, including reducing oxidative stress and inflammation, supporting cognitive function, and lowering the risk of neurodegenerative diseases. These diets also promote a healthy gut-brain axis and improve vascular health, contributing to overall brain health.

However, careful planning and awareness of potential accessibility barriers are essential to prevent nutrient deficiencies, primarily in omega-3 fatty acids, vitamin B12, iron, zinc, selenium, and iodin