According to both a Harvard nutritionist and a neurologist, this is the best food for maintaining brain health.

Both a Harvard nutritionist and a neurologist might agree that certain foods are particularly beneficial for maintaining brain health. One food that often receives praise in this regard is fatty fish, such as salmon, mackerel, sardines, and trout. 

Fatty fish are rich sources of omega-3 fatty acids, specifically EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), which are essential for brain health. These omega-3 fatty acids play crucial roles in brain function and development, including supporting nerve cell communication, reducing inflammation, and promoting neuroplasticity.

Studies have shown that regular consumption of fatty fish or omega-3 supplements may help protect against age-related cognitive decline, reduce the risk of developing neurodegenerative diseases like Alzheimer's and Parkinson's, and improve overall cognitive function and mood.

Additionally, fatty fish are also excellent sources of high-quality protein, vitamins (such as vitamin D), and minerals (such as selenium), which further contribute to overall brain health.

Therefore, including fatty fish in your diet regularly, at least two servings per week as recommended by dietary guidelines, can be a valuable component of a brain-healthy diet.