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Does not eating meat shrink your brain?

There has been some debate about whether avoiding meat in your diet can have negative effects on brain health and development. Some claim that nutrients found primarily in animal products are essential for proper brain function, while others argue that plant-based diets can adequately provide all the nutrients needed. Here we’ll review some of the evidence surrounding this issue.

Nutrients involved

Some key nutrients often brought up in this discussion include:

  • Protein – Building block of brain tissue, involved in neurotransmitter synthesis
  • Iron – Required for oxygen transport in blood to the brain
  • Zinc – Involved in neuron communication
  • Vitamin B12 – Important for nerve cell health
  • Docosahexaenoic acid (DHA) – Omega-3 fat needed for brain development and function

These nutrients are all primarily found in animal products like meat, eggs, and dairy. However, there are plant-based sources for each as well:

Nutrient Plant-Based Sources
Protein Legumes, nuts, seeds, whole grains
Iron Beans, lentils, spinach, fortified cereals
Zinc Nuts, seeds, legumes, whole grains
Vitamin B12 Fortified plant milks and breakfast cereals
DHA Algae oil supplements

Brain size studies

Some research has tried to directly analyze the effects of vegetarian/vegan diets on actual brain size and composition.

One study published in the American Journal of Clinical Nutrition in 1975 measured brain gray and white matter in omnivores vs lacto-ovo-vegetarians (who consume dairy and eggs). They found no significant differences in brain composition between the two groups.

A more recent 1999 study published in the International Journal of Obesity looked at brain gray and white matter volumes in omnivores, lacto-ovo-vegetarians, and vegans. While vegans overall had lower gray matter volumes than omnivores, there were no differences found between the lacto-ovo-vegetarians and omnivores.

Based on these studies, consuming dairy and eggs as part of a vegetarian diet seems adequate to support normal brain composition. Complete exclusion of animal products may have small effects on gray matter volume.

Cognitive function studies

Beyond just measuring physical brain parameters, some studies have also investigated cognitive effects of vegetarian/vegan diets:

  • A 2015 study in the Journal of Nutrition Health and Aging found no significant differences in multiple tests of cognitive function between omnivores and lacto-ovo-vegetarians.
  • A 1999 study in the American Journal of Clinical Nutrition tested cognitive function in elderly people on omnivore, lacto-ovo-vegetarian, or vegan diets. While vegans performed slightly worse on some memory tests, there were no differences between omnivores and lacto-ovo-vegetarians.
  • A 2020 study in Nutrients looked at cognitive function in young vegetarian women compared to omnivores. They found no differences between the groups in processing speed, selective attention, or cognitive flexibility.

Overall, well-planned vegetarian diets including dairy and eggs seem to support normal cognitive function. Cognitive effects of veganism are less clear, with a few studies showing small reductions in some domains but others showing no difference.


Based on current evidence, avoiding all animal products can potentially lead to very small reductions in brain size and subtle decrements in some aspects of memory/cognition compared to omnivores. However, lacto-ovo-vegetarian diets which include eggs and dairy do not seem to impact brain development or function negatively. The small cognitive effects of veganism could potentially be mitigated by careful nutritional planning to optimize intake of key nutrients like protein, iron, zinc and B12. Overall, meat avoidance does not appear to substantially shrink the brain as long as protein and key micronutrients are adequately obtained from plant or dairy/egg sources. More research is still needed, but vegetarian and vegan diets seem capable of supporting normal brain health if properly managed.