Among these, dietary protein has emerged as a potential protective factor given its role in muscle and organ building, tissue and cell repair and the production of neurotransmitters that influence cognitive processes from memory to mood.
While much of the associations to date are observational in nature, a recent review published by Cambridge University Press set out to explore the longer-term effects of dietary protein on measures of cognitive performance through an assessment of randomized controlled trials in diverse populations.
“Currently, no recommendations exist regarding protein intake for cognitive health, but higher-protein diets could be a strategic approach to slow down or prevent cognitive decline,” the team of Dutch researchers from the NUTRIM Institute of Nutrition and Translational Research in Metabolism at Maastricht University Medical Center+ wrote in Nutrition Research Reviews.
Their review considered data from 26 trials identified through a systematic search of the Embase, Medline and Cochrane databases up until July 2023.
The potential of intact protein
Studies selected compared either an intact protein supplement or protein-rich food with a non-protein or lower-protein control, or compared two intact proteins with one another.
Dose and type of protein, along with changes in cerebral blood flow (CBF), were assessed in relation to cognitive performance tests on three cognitive domains: psychomotor speed and attention, executive function and memory, and global cognition. CBF is a validated marker of brain vascular function, which has been suggested to play an important role in cognitive health.
“To improve cognitive performance, the mechanisms underlying a protein’s ability to enhance CBF may be influenced by both the amount and source of dietary protein,” the researchers wrote. “No comprehensive reviews of RCT have evaluated the potential role of dietary proteins in improving CBF and, by extension, cognitive performance, nor have they compared the efficacy of different protein sources in this regard.”
They noted that previous reviews have focused on the effects of specific amino acids rather than an intact protein, lacked RCT evidence and did not assess brain vascular function.
Considering the data
Of the papers included in the review, 23 reported the effects on cognitive performance and three on cerebral blood flow (CBF).
“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,” the researchers reported. “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.”
Considering the data, they suggested that increased dietary protein intake may be more beneficial in some populations than others. Given that normal aging leads to a decline in CBF, they hypothesized that “older adults may have more room to improve in certain cognitive domains, such as psychomotor speed and memory.” The study also noted that stroke survivors or people with dementia may see more gains than healthy individuals.
“Animal studies have shown that stroke can lead to significant decreases in brain protein synthesis,” the researchers wrote. “Potential improvements in brain protein synthesis and rehabilitation, neuron energy formation and neurotransmitter synthesis through improvements in amino acid bioavailability could, in turn, lead to improvements in CBF.”
In the three studies involving CBF, increased regional blood flow was associated with most cognitive performance outcomes.
“The comparative effects of different protein types warrant further investigation,” the researchers concluded. “Overall, this review encourages additional research into protein-rich foods or supplements which could potentially prevent or mitigate cognitive decline.”
Source: Nutrition Research Reviews, doi: 10.1017/S0954422424000271, “Effects of Dietary Proteins on Cognitive Performance and Brain Vascular Function in Adults: A Systematic Review of Randomised Controlled Trials”, Authors: Micah Adams et al.