- A new review investigates whether influencing the makeup of the gut microbiome can improve brain health.
- Specifically, it focuses on probiotics, prebiotics, dietary changes, and fecal microbiota transplants (FMT).
- The authors conclude that modulating the gut microbiome may slow cognitive decline and improve brain health.
- This effect may be due to reduced inflammation in the brain, altered neurotransmitter signaling, and increased levels of microbial metabolites.
If a nutrition or wellness trend becomes popular on social media, it is best to remain skeptical. Much of the content shared is inaccurate at best and downright wrong at worst.
Gut health, however, bucks this trend. While gut microbes have become internet darlings, the evidence of their widespread importance in overall health continues to stack up.
A new review on probiotics and cognitive health adds to this growing stack. The study appears in the journal Nutrition Research.
Although the authors call for more research, their conclusions are positive. They find that modulating the gut microbiome might help older adults with early cognitive decline improve their thinking skills.
Overall, this is still a very young field, and there is much work to be done, but they conclude that “microbiota modulation is a promising therapeutic target that complements existing pharmacological and lifestyle interventions.”
A few decades ago, if someone had claimed that bacteria in the colon could slow cognitive decline or support mental health, it would have been considered fringe and likely raised a few eyebrows.
Today, this is not far-fetched in the least. While understanding the precise relationships will take many years, it is now well within the realms of mainstream science.
Each one of us harbours trillions of microbes in our gut. They aid digestion, help us manufacture vitamins, and produce a suite of compounds that support our health.
We now know that they can also converse with the brain via multiple pathways, known as the gut-brain axis.
One of these lines of communication is the vagus nerve, which travels between the gut and the brain. Another is through compounds, such as short-chain fatty acids (SCFAs) that bacteria produce as they ferment fiber.
SCFAs can stimulate the vagus nerve directly, but they can also travel to the brain via our bloodstream.
As we age, our cognitive abilities tend to slow. However, some decline faster than others, and some will eventually progress from cognitive decline to dementia.
As populations become steadily older, understanding risk factors and lifestyle interventions that might ease the burden is of increasing importance. Some scientists are turning to the power of microbes.
Probiotics are live bacteria that, when consumed in large enough amounts, provide health benefits. Anyone who has visited a store recently will likely have seen probiotics in pills, shakes, toothpaste, and everything in between.
Overall, evidence that store-bought probiotics support health is fairly weak, especially in people who are already healthy. Outside of some quite specific cases — such as antibiotic-associated diarrhea — they have not demonstrated much success at treating health conditions.
However, this is to be expected. There are hundreds of species of bacteria in the human gut, and everyone’s microbiome is unique.
Even identical twins, who are essentially genetic clones, have distinct gut microbes. Therefore, it is no surprise that adding a few strains of microbes does not have a measurable effect for everyone.
This does not make the approach useless, though. The more we understand, the more likely it is that we will discover the species, strains, or doses needed to produce specific benefits.
Other than probiotic foods and drinks, other techniques are also popular. Prebiotics, for instance, are essentially food for bacteria.
If you consume more prebiotics — such as dietary fiber — it will support the growth of “good” gut bacteria more generally.
The recent review looks at a range of approaches for maintaining cognitive health as we age: using probiotics, prebiotics, dietary interventions, and FMT. The authors also discuss the mechanisms through which these approached might protect cognitive health.
The review included data from 15 studies in 10 countries and more than 4,200 participants aged 45 or older. Here are their conclusions:
Dietary interventions
The latter include B12, folate, choline, and methionine. These compounds support functions such as gene expression and energy production.
Overall, the authors concluded that dietary interventions have the potential to remodel the gut microbiome, increase the production of SCFAs, and stabilize neurotransmitter networks.
They can also promote cognitive health and reduce inflammation in the brain. This is important, as increasing evidence suggests that neuroinflammation plays a significant role in mental health disorders and cognitive decline.
Probiotics and synbiotics
In this category, the authors conclude that probiotics and synbiotics may improve verbal fluency and executive function, which includes working memory and cognitive flexibility.
They also find that these interventions increased the diversity of the gut microbiome, which is a measure of microbiome health, and altered neurotransmitter pathways.
FMT
There have been far fewer studies on FMT than the other interventions, but the authors describe the results as “preliminary but striking.”
The study included in the review recruited people with Alzheimer’s disease. FMT was associated with a more rapid change in the gut microbiome than probiotics, synbiotics, or dietary interventions.
Most importantly, the study also measured improvements in cognitive performance and other measures of cognitive decline. However, more research is needed.
The conclusions of this review are upbeat. They hint at the possibility we might one day modulate the gut microbiome in such a way that we slow dementia and keep minds sharp as they age. However, we are not there yet.
The studies included in this review are mostly small and short-term.
Commercially available probiotics, as it currently stands, are not selected solely because of their potential health benefits.
Instead, they are the ones deemed safe for human consumption. This means that, while some probiotics could improve brain health, they might not be available for sale.
As for FMT, this is not something that is easily accessible. That leaves dietary interventions, which we have much more control over.
Medical News Today spoke to Federica Amati, PhD, MPH, RNutr, about how best to improve the health of our gut microbiome through diet.
Amati, who was not involved in the review, is a medical scientist, registered public health nutritionist, and research fellow at the School of Public Health, Faculty of Medicine, Imperial College London, in the United Kingdom.
“In the U.K. and U.S., the vast majority of people do not consume enough fiber. This directly impacts the health of our gut microbiome: Without fiber, our gut bacteria have nothing to eat,” she told us.
Fiber is found in essentially all plants, and Amati suggested aiming to eat 30 different plants per week. “This matters because there is a wide range of fiber types, and different microbes have different preferences. Consuming a range of plants ensures they all get supported,” she explained.
She also suggested limiting intake of ultra-processed foods where possible. These products do not contain enough fiber to support “good” microbes, but they do contain long lists of additives that can harm microbes, and their sugar and fat content can also encourage the growth of “bad” gut bacteria.
“Fermented foods are also a great choice. They naturally contain probiotics, often in much greater variety than commercially available probiotic supplements. Fermented vegetables, like kimchi or sauerkraut, are particularly good because they are fermented plants, so they’re a natural synbiotic.”
– Federica Amati, PhD, MPH, RNutr
