A study involving 99 healthy older adults found that levels of monounsaturated fatty acids were associated with cognitive performance and the organization of the brain's attention network.

MUFAs are found in olive oils, nuts and avocados, and are a component of the Mediterranean diet, which has been associated with slower cognitive decline and lower dementia risk.

The study found that general intelligence was associated with how efficiently the dorsal attention network was functionally organized used a measure called small-world propensity, which describes how well the neural network is connected within locally clustered regions as well as across globally integrated systems.

In turn, they found that those with higher levels of MUFAs in their blood had greater small-world propensity in their dorsal attention network, suggesting that this is part of the reason for the link between diet and cognition.

And in another study by the same researchers, involving 94 older adults (65-75), blood levels of three omega-3 fatty acids (ALA, stearidonic acid and ecosatrienoic acid) were associated with levels of fluid intelligence, and this was mediated by the size of the left frontoparietal cortex. A larger left frontoparietal cortex was associated with higher levels of the omega-3 acids and better performance on tests of fluid intelligence.

A second study found that the size of a brain region called the fornix was associated with a balance of omega-3 and omega-6 fatty acids in the blood, and a more robust fornix was linked to better memory. The fornix is one of the first brain regions to be compromised in Alzheimer's disease.