A new study published in Nature Communications suggests that a daily fiber supplement could improve brain function in older adults. Researchers found that in just 12 weeks, participants who took the supplement showed better performance in memory tests that are often used to detect early signs of Alzheimer’s disease. This placebo-controlled, double-blind trial was conducted on twins over the age of 65, offering insight into how gut microbiome interventions could benefit cognitive health in older adults.
As the global population ages, more people are experiencing cognitive decline, which often progresses into dementia. With rates of Alzheimer’s disease and other forms of dementia expected to rise, there is a growing interest in finding ways to preserve cognitive function in older adults. Currently, exercise and a healthy diet are known to slow some of the effects of aging, but many older adults face challenges in sticking to exercise routines.
In recent years, researchers have also started exploring the link between gut health and brain health, known as the gut-brain axis. The gut microbiome—the community of microbes in the digestive system—plays a critical role in overall health. Some research suggests that changes in the gut microbiome could contribute to conditions like Alzheimer’s disease, though the exact mechanisms are still being studied.
The new study aimed to test whether modulating the gut microbiome through a fiber supplement could improve cognitive function in older adults. The hope was that a simple and affordable intervention could help maintain or even improve brain health in an aging population.
“We know the gut microbiome plays a role in so many processes in the body, but we are still in the early stages of trying to really understand how this works. Ageing brings with it many challenges and we lack treatment options for many age-associated issues, such as the loss of muscle as we age, and changes in our cognition,” said study author Mary Ní Lochlainn, a NIHR clinical lecturer at King’s College London and specialist registrar in geriatric, stroke, and general internal medicine at Guy’s and St Thomas’ NHS Foundation Trust.
“The exciting thing is that the gut microbiome can be influenced from the outside (for example with prebiotics or probiotics), and so could be a target for treatments which aim to improve these age-associated conditions, a potential untapped resource!”
To test their hypothesis, the researchers conducted a randomized, placebo-controlled trial with 72 twins aged 65 or older. Using twins allowed them to control for genetic and environmental factors, making it easier to detect the effects of the fiber supplement. Half of the participants received a fiber supplement that included prebiotics—compounds that promote the growth of beneficial gut bacteria—while the other half received a placebo.
Participants were instructed to take one sachet of their assigned supplement each day for 12 weeks. The fiber supplement contained inulin and fructo-oligosaccharides, both of which are known to nourish beneficial bacteria in the gut. The placebo contained a simple carbohydrate, maltodextrin, which does not have the same prebiotic effects.
All participants were also encouraged to engage in resistance exercises, which have been shown to improve muscle strength and overall health in older adults. The study was conducted remotely, with participants completing cognitive tests and providing stool samples for gut microbiome analysis from their homes. The cognitive tests focused on memory and problem-solving skills, while the stool samples were used to assess changes in the gut microbiome over the course of the study.
After 12 weeks, the participants who took the fiber supplement showed significant improvements in memory tests compared to those who took the placebo. Specifically, they made fewer errors on a test called Paired Associates Learning, which measures visual memory and the ability to learn new information. This particular test is considered an early marker of Alzheimer’s disease, suggesting that the fiber supplement may have protective effects against cognitive decline.
“We knew the potential was there to see an improvement in cognition but the timeframe was surprising,” Lochlainn told PsyPost. “We weren’t sure whether 12 weeks was too short, and so we were pleasantly surprised to see some benefits in this relatively short time frame.”
The researchers also found changes in the gut microbiome of participants who took the fiber supplement. These participants had higher levels of Bifidobacterium, a type of bacteria known for its beneficial effects on gut health. Previous studies have suggested that Bifidobacterium may help reduce inflammation, which is believed to play a role in both cognitive decline and conditions like Alzheimer’s.
The findings indicate “that there is some evidence that a cheap fibrous prebiotic food supplement has the potential to improve cognition, and that it is well tolerated with minimal risk,” Lochlainn said.
However, despite these positive findings for brain health, the study did not find any significant differences in physical strength between the two groups. The researchers had hoped that the fiber supplement might also improve muscle function, but tests like chair-rise time and grip strength showed no notable differences.
While the results of the study are promising, there are several limitations that need to be considered. First, the study was relatively small, with only 72 participants. Although the twin design provided a strong control for genetic and environmental factors, larger studies are needed to confirm the findings. Additionally, the 12-week duration of the study may not have been long enough to fully assess the effects of the supplement on muscle strength, which can take longer to show measurable improvements.
“We really need larger scale studies before we can be sure how much of an effect these prebiotics have on cognition,” Lochlainn said.
Another limitation is the study’s focus on healthy older adults. Future research should explore whether the same intervention could benefit people with more advanced cognitive decline or those at higher risk for Alzheimer’s disease. The researchers also suggested that longer trials could provide more insight into how gut microbiome changes over time and whether sustained improvements in cognitive function can be achieved.
One important area for future research is determining the optimal dosage of fiber supplements for improving both cognitive and physical health. While the 7.5-gram dose used in this study was effective for improving cognition, it may not have been enough to impact muscle strength. Exploring different types of prebiotics and dosages could help identify the most effective interventions for older adults.
“We want to explore these supplements further, staying in the realm of ageing, but considering clinical populations, for example, to help older people build up further resilience for undergoing planned surgery,” Lochlainn explained.
“While we are still learning about the benefits of supplements which aim to target the bacteria in the gut, one thing we are sure of is the benefits of resistance exercise for staying healthy as we age,” she added. “The NHS website has a good selection of strength exercises, as well as balance exercises, which are a great place to start for anyone thinking about maintaining their independence into old age.”
The study, “Effect of gut microbiome modulation on muscle function and cognition: the PROMOTe randomised controlled trial,” was authored by Mary Ni Lochlainn, Ruth C. E. Bowyer, Janne Marie Moll, María Paz García, Samuel Wadge, Andrei-Florin Baleanu, Ayrun Nessa, Alyce Sheedy, Gulsah Akdag, Deborah Hart, Giulia Raffaele, Paul T. Seed, Caroline Murphy, Stephen D. R. Harridge, Ailsa A. Welch, Carolyn Greig, Kevin Whelan, and Claire J. Steves.
