What’s good for your aging gut may also be good for your aging brain. A first-of-its-kind study in twins found that taking daily protein and prebiotic supplements can improve memory test scores in people over age 60.
Published early last year, the findings are food for thought, especially as the same visual memory and learning test is used to detect early signs of Alzheimer’s disease.
The double-blind trial tested two inexpensive plant-fiber prebiotics that are available over the counter in many countries.
Prebiotics are non-digestible consumables that help stimulate our gut microbes.
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One of the supplements was inulin, a dietary fiber in the fructan class. The other, fructooligosaccharide (FOS), is a plant carbohydrate often used as a natural low-calorie sweetener.
Watch the video below for a summary of the research:
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To look into how these supplements affect the aging brain, researchers at King’s College London enrolled 36 pairs of twins, all at least 60 years old.
Each duo was randomly split: one twin received a daily prebiotic mixed into protein powder, while the other received a placebo powder.
The twins who unknowingly took inulin or FOS generally scored higher on a cognitive test three months later.
What’s more, the daily fiber supplements were linked to subtle changes in the gut microbiome between twins.
The beneficial Bifidobacterium, for instance, were more plentiful in those taking inulin or FOS.
Studies on mice suggest Bifidobacterium reduces cognitive deficits by regulating gut-brain connections.
“We are excited to see these changes in just 12 weeks. This holds huge promise for enhancing brain health and memory in our aging population,” said Mary Ni Lochlainn, a geriatric medicine researcher at King’s College London, when the findings were published in 2024.
“Unlocking the secrets of the gut-brain axis could offer new approaches for living more healthily for longer.”
King’s College is home to the United Kingdom’s largest adult twin registry, and twin studies are highly valuable when it comes to differentiating between the effect of genetics and the environment on human health.
Past studies on rodents suggest that high-fiber supplements, like inulin and FOS, can ‘feed’ the colon’s microbiome, allowing ‘good’ bacteria to thrive.
Some of these bacterial players are also linked to improved cognitive function in both mice and humans.
Evidence for the close relationship between the gut and the brain is growing year after year. Some experts are now so convinced by the results, they refer to the gut as the body’s ‘second brain’.
But the way these two nervous systems work together remains a mystery.
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The twin study at KCL hints that consuming certain ‘brain foods’ could be a promising way to treat cognitive decline, adding to research suggesting key food nutrients may be able to slow its progress.
“These plant fibers, which are cheap and available over the counter, could benefit a wide group of people in these cash-strapped times. They are safe and acceptable too,” said geriatrician Claire Steves at KCL.
“Our next task is to see whether these effects are sustained over longer periods and in larger groups of people.”
While prebiotics appeared to improve some aspects of cognitive function in an aging brain, like memory and processing times, the study didn’t identify significant physical benefits.
Muscle loss didn’t improve among aging twins taking high-fiber supplements, although inulin and FOS are important factors in musculoskeletal maintenance.
The twins that participated in the current trial were mostly female, and even though the researchers adjusted for sex differences in their findings, they acknowledge that there may be some selection bias amongst KCL’s twin cohort.
That said, females are more susceptible to Alzheimer’s disease, and studies like this one support the emerging idea that cognitive decline is not always a disease of the brain, but may involve external factors, too.
Related: Levels of Omega-3 Could Help Explain Women’s Alzheimer’s Risk
In 2025, researchers reported that in humans and mice, a lower ratio of Bifidobacterium to Akkermansia in the gut bacteria is linked to multiple sclerosis, and this imbalance was also associated with more severe disease.
The gut has its fingers in many bodily ‘pies’, including the immune system and the central nervous system. Feeding its microbiome certain prebiotics and probiotics could open the door to treating a plethora of illnesses and diseases.
The study was published in Nature Communications.
An earlier version of this article was published in March 2024.
