Seafood is well-recognized for its brain health benefits, but researchers wonder if these benefits outweigh the risks of mercury exposure. In this study, scientists analyzed 44 papers on 102,944 mother-child pairs and 25,031 children. They found consistent evidence of brain health benefits for children when mothers ate seafood while pregnant, and that benefits began even at the lowest amounts of seafood (about 4 oz /week). No negative impacts on neurocognitive development were noted even at the highest levels of seafood consumption (more than 12 ounces per week).
Prostaglandins Leukotrienes, and Essential Fatty Acids. 2019 Oct 11;151:14-36. doi: 10.1016/j.plefa.2019.10.002. (Hibbeln CJR et al.)

What nourishes your body can also help nourish your brain as well. In this study, researchers analyzed the eating habits and brain function of more than 1,400 older adults. In the adults aged at least 70 years old, closely following a Mediterranean diet was linked with improvements in global cognitive function, visual-spatial organization, memory, scanning, and tracking. However, the results were not statistically significant in the adults younger than age 70, or in the group as a whole.
Nutritional Neuroscience. 2019 Aug 21. doi: 10.1080/1028415X.2019.1655201. (Wade AT et al.)

While there is much to learn about preventing dementia and cognitive decline, the Mediterranean diet seems to show promise in protecting brain health across the lifespan. In this study, scientists analyzed the eating habits of 2,621 adults at ages 25, 32, and 45 years, then analyzed their brain function at ages 50 and 55. Those most closely following a Mediterranean diet had a 46% lower risk of having poor cognitive function. Those whose diets scored highly on the A Priori Diet Quality Score (a measure of how nutritious your diet is) also had a reduced risk of poor cognitive function, while the DASH diet (a healthy diet to prevent high blood pressure) did not show a significant relationship with brain health.
Neurology. 2019 Apr 2;92(14):e1589-e1599. doi: 10.1212/WNL.0000000000007243. (McEvoy CT et al.)

Numerous studies have observed a link between the Mediterranean Diet and slower cognitive decline, but researchers wonder how this might relate to the development of Alzheimer’s disease. To better understand diet’s relationship with Alzheimer’s pathology, scientists analyzed the eating patterns and buildup of Aβ (small pieces of protein that can accumulate in the brain, potentially creating plaques and causing brain cells to be destroyed) in 77 older adults who were already on the path to Alzheimer’s disease (by being flagged as being Aβ accumulators). Those most closing following a Mediterranean diet had significantly less Aβ accumulation over time, with fruit standing out as a particularly beneficial food. The authors suggest that improving your Mediterranean diet score by just 1 point (0-9 point scale) may result in a 20% decrease in Aβ accumulation over 1 year, and up to a 60% decrease over 3 years.
Translational Psychiatry. 2018 Oct 30;8(1):238. doi: 10.1038/s41398-018-0293-5. (Rainey-Smith SR et al.)

Stroke survivors are twice as likely to develop dementia compared to the general population. To see how diet relates to brain health in stroke survivors, researchers analyzed the eating patterns and brain function of 106 stroke survivors for more than 4 years. Those most closely following a “MIND diet” had a slower rate of cognitive decline than those who don’t follow a MIND diet. The MIND diet is a hybrid Mediterranean-DASH diet that emphasizes foods associated with brain health, including whole grains, green leafy vegetables, berries, nuts, olive oil, and fish. The Mediterranean diet is well-known for its brain benefits, so it’s not surprising that this new diet inspired by the Mediterranean diet is also showing promise for brain health. 
Presentation at the American Heart Association Meeting. Los Angeles, California. January 25, 2018.