Effects of dietary proteins on cognitive performance and brain vascular function in adults: a systematic review of randomised controlled trials.

The incidence of cognitive decline is rising, leading to increased attention on the preventive role of healthy foods on brain function. Previous reviews including primarily observational studies suggested that dietary proteins may improve cognitive performance, but evidence from individual randomised controlled trials (RCT) is less consistent. Therefore, this systematic review examined the long-term effects of dietary proteins from RCT, considering both their amount and type, on cognitive performance (psychomotor speed and attention, executive function, memory and global cognition). Alterations in cerebral blood flow (CBF) - a validated brain vascular function marker - were also considered. A total of 4747 studies were identified through a systematic search, resulting in twenty-three included papers reporting effects on cognitive performance (n = 23) and CBF (n = 3). Improvements were observed in three out of the nine studies that evaluated psychomotor speed which compared a dietary protein intervention with a non-protein or lower-protein control. Of the six beneficial observations on working memory (n = 12), declarative memory (n = 10) and visuospatial memory (n = 10), five were nut interventions from three different trials. Limited studies focusing on global cognition suggested that specific target populations, namely subacute stroke or dementia, may benefit more than healthy individuals from increased dietary protein intake. From the three studies involving CBF, improvements in regional blood flow were associated with most cognitive performance outcomes. The comparative effects of different protein types warrant further investigation. Overall, this review encourages additional research into protein-rich foods or supplements which could potentially prevent or mitigate cognitive decline.