How gut health can impact the brain

Over the last few years, there has been growing interest in improving gut health, with research suggesting that the bacteria in your gut can impact your physical and mental health. Recently, new research has focused on how the gut microbiome — which includes bacteria, fungi, and more — can impact brain health.

According to a new study published in Nature, changes to the gut microbiome could contribute to memory loss as people age. For the study, researchers had young and old mice live together and observed the effect on the older mice's microbiome. Because mice are coprophagic, or eat each other's poop, their microbiomes will eventually affect each other and average out. 

After just a month of living together, researchers were surprised to find that the young mice that were "otherwise totally healthy" started to show signs of severe memory impairment.

"[W]hen we tested the young mice that were living with old mice, they were basically identical to the old mice in terms of performance," said Timothy Cox, an MD/PhD student at the University of Pennsylvania and one of the study's authors. "They did really poorly on the standard [memory] test."

The researchers later identified a potential gut bacterium called Parabacteroides goldsteinii that could have a negative impact on cognition over time. P goldsteinii is involved in the production of medium-chain fatty acids (MCFAs), which accumulate with age and activate gut-resident myeloid immune cells to trigger inflammation. The researchers traced the effect of MCFAs from intestinal immune cells to sensory neurons and up to the vagus nerve into the hippocampus, which is the part of the brain where memory is formed. 

"The function of vagal afferent neurons is impaired, the interoceptive signal received by the brain is weakened, and hippocampal function declines," the researchers wrote.

Overall, the researchers identified six gut markers that distinguished participants who were cognitively healthy and those with either subjective or objectively measured cognitive impairments. The six markers were:

• 5-hydroxyindole acetic acid
• Indole-3-propionic acid
• Choline
• Indoxyl sulfate
• Kynurenic acid
• Kynurenine

According to David Vauzour, one of the study's authors from the University of East Anglia in England, the six gut markers reflect early metabolic disruption in the gut-brain axis. "These results highlight that metabolic alterations appear long before cognitive decline is clinically apparent, offering a noninvasive and scalable approach for early risk identification," he said.

Vauzour also noted that since these gut markers "integrate both gut microbial activity and host physiology, they outperform microbiome-only metrics and offer promising avenues for early detection, monitoring, and targeted intervention strategies."

More research is needed on gut health

However, Karen Corbin, an investigator at the AdventHealth Research Institute of Metabolism and Diabetes, noted "there's no clear definition of a healthy gut microbiome," which makes it harder to know what will affect the gut and how changes in the gut will impact the rest of the body. Many factors, including genes, diet, environment, and even pets, can affect the makeup and balance of people's microbiomes. 

Separately, Daniel Freedberg, a gastroenterologist at Columbia University, said that there are "a lot of tall claims based on animal studies that the microbiome influences diabetes or obesity or whatever," but it's "really unlikely" that these findings translate to humans.

If you want to improve your gut health, health experts recommend eating a healthy diet filled with fruits, vegetables, whole grains, and legumes. Similarly, key elements of a "brain boosting" diet include leafy greens, colorful fruits and vegetables, fish, nuts, whole grains, legumes, and olive oil.