The relationship between diet, micronutrient status, and the gut-brain axis has been a topic of interest in recent research. The gut-brain axis is a biochemical signaling pathway connecting the gastrointestinal (GI) microbiome and certain aspects of brain function and mood. It is believed to influence cognitive function and mood through mechanisms related to the immune system, inflammation modulation, and cellular metabolism.  

Polyphenols are bioactive compounds found in fruits, vegetables, seeds, coffee, and cocoa, and they have been shown to support brain function and the gut-brain axis. They have also been shown to support the body’s response to oxidative stress and inflammation. In regard to neuronal and brain health, they have been shown to support cerebrovascular flow, neuronal signaling, and neurogenesis. 

Research indicates that polyphenols may support a healthy gut microbiome. An estimated 90% of dietary polyphenols are not digested in the small intestine and may therefore influence the microbiota in the colon. They have been shown to support healthy populations of certain beneficial bacteria, such as Bifidobacterium and Lactobacillus. Certain polyphenols (such as resveratrol) have also been shown to help support healthy levels of inflammatory cytokines and may help improve microbial dysbiosis. 

Animal studies have also indicated that certain polyphenols may influence the population of short-chain fatty acid (SCFA)-producing bacteria. SCFAs have been shown to benefit neuronal health in many ways, including their ability to help modulate nervous system signaling and serotonin release.  

A recent review by Horn and colleagues published in Translational Psychiatry explored the interplay between diet, the gut microbiome, and the pathophysiology of some mental disorders. An animal study investigated the effect of polyphenol-rich extracts from grape and blueberry (PEGB) on cognitive decline and neuronal function in aged mice. Adult mice were fed PEGB-rich diets for 14 weeks. Improvements in survival rate, memory, learning, and nerve generation were observed.  

Horn and colleagues describe studies related to cognitive decline and polyphenol use in clinical trials. One randomized, parallel-group clinical trial involving more than 400 healthy participants explored the impact of a Mediterranean diet supplemented with mixed nuts or extra virgin olive oil on cognitive decline. The study lasted for greater than 5 years and concluded that Mediterranean diets supplemented with olive oil or nuts may help support the prevention of age-related cognitive decline.  

Age-related cognitive decline has been associated with neuroinflammation and oxidative stress. Diets rich in polyphenols may support a healthy GI microbiome. They may also support neuronal health, cognitive health, and healthy aging. 

By Colleen Ambrose, ND, MAT