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Research shows that more dietary fiber could improve cognitive function. Stefania Pelfini, La Waziya Photography/Getty Images
  • Diseases such as dementia and Alzheimer’s disease can cause the normal mild cognitive decline of an aging brain to worsen.
  • There is currently no cure for dementia or Alzheimer’s disease.
  • Researchers from King’s College London have found that taking a dietary fiber supplement may help improve brain function in older adults.

As we age, all parts of the body — including the brain — begin to slow down. It is normal for a person to have trouble multitasking, finding certain words, or remembering names in a healthy aging brain.

In some cases, diseases such as dementia and Alzheimer’s disease can cause mild cognitive decline of an aging brain to worsen. This can lead to more serious issues including memory loss, inability to plan or solve problems, speaking or writing difficulties, mood changes, anxiety, sleeping issues, and confusion with places, dates, and times.

While there is currently no cure for dementia or Alzheimer’s disease, adopting healthy lifestyle choices and certain medications may help slow its progression.

Now, researchers from King’s College London have found that taking a dietary fiber supplement may help improve brain function in older adults.

Scientists also found that the fiber supplements did not affect participants’ muscle strength.

The study was recently published in the journal Nature Communications.

According to the World Health Organization, the world’s population is aging at a more rapid rate than in the past and people are living to a much older age. The number of people aged 60 and older globally was about 1.4 billion in 2022 and is expected to hit 2.1 billion by 2050.

With this increase in aging worldwide, it is important to have new ways to combat age-related conditions such as cognitive decline, Dr. Claire Steves, professor of aging and health and head of the Department of Twin Research & Genetic Epidemiology at King’s College London and senior author of this study told Medical News Today.

“With this comes an increase in the number of age-related conditions, which have a major impact on the ability of older people to continue to live well independently,” Dr. Steves continued.

“We lack effective treatments for many age-related conditions, so it is really important that we focus our energies in this area. We need to research these topics more to expand our knowledge on ways to prevent, slow, and indeed reverse age-associated declines, wherever possible,” she said.

For this study, Dr. Steves and her team focused on two prebiotic supplements — the dietary fiber inulin and the plant-based carbohydrate fructooligosaccharides (FOS).

“Research in recent years has shown that the bacteria within our guts, known as the gut microbiome, are linked to our health and well-being. Studies have shown connections between these bacteria and the brain, known as the gut-brain axis. Connections have also been shown with other organs including with muscle health. We decided to test whether improving the health of the gut bacteria using a prebiotic could improve brain and muscle function,” Dr. Steves explained.

“We know that inulin and FOS are safe, cheaply accessible, commercially available prebiotic supplements associated with healthy gut bacteria. We were also influenced by another trial which looked at inulin and FOS in a nursing home population. They showed improvements in hand grip strength, exhaustion levels, and overall measures of frailty, in those who had the inulin and FOS supplement,” she continued.

Previous studies have found that inulin changes the gut microbiome, helps reduce neuroinflammation, and improves traumatic brain injury recovery.

Research regarding FOS has reported the supplement may help weaken the development of Alzheimer’s disease by reducing beta-amyloid in the brain, and assist with lowering neuroinflammation and improving memory.

Researchers recruited 36 pairs of twins over the age of 60 for this study. One twin in each pair was given a dietary fiber supplement each day for 12 weeks, while the other twin received a placebo.

Scientists monitored the study participants through video, online questionnaires, and cognitive tests. Additionally, participants were asked to participate in resistance exercises and also ate a protein supplement aimed at improving muscle function.

The study was double-blind in which neither the analysis team nor the study participants knew which they received until the study was finished.

At the study’s conclusion, researchers found the group receiving a fiber supplement had improved performance in brain function assessment tests, including the Paired Associates Learning test — an early marker for Alzheimer’s disease — as well as reaction time and processing speed tests.

“We were pleasantly surprised to find that those who received the prebiotic supplement had an improvement in memory and thinking tests compared to the placebo, over a 12-week time frame,” Dr. Steves said. “We know there is a connection between the gut bacteria and the brain, so this study provides further evidence of this link, and is hugely promising for future studies aiming to improve memory and prevent declines with age.”

“We have shown that a simple, cheap, and accessible fiber supplement, which leads to increased numbers of healthy bacteria in the gut, can actually influence brain function and memory test results,” she added. “Seeing this positive result in just three months holds huge promise for enhancing memory and brain health in our aging population.”

The scientists did report there was no significant difference in muscle strength between the supplement and placebo groups.

MNT also spoke with Dr. Clifford Segil, a neurologist at Providence Saint John’s Health Center in Santa Monica, CA, about this study.

Dr. Segil said he agreed with the study authors that it’s difficult to report improvements in cognition and for the study to have clinical meaningfulness at this stage.

“Even after reading the study, I like to say you are what you eat, but sometimes your brain is not what you eat so it’s hard to say that changing your diet is going to make you not age, have better muscles, and better cognition,” he explained.

“Although, poor diets are associated with diabetes, high blood pressure, and cardiovascular and heart risk factors. So even though I can’t say adding fiber may or may not help, there’s clearly things that you shouldn’t eat — it’s harder to say what you should eat,” he added.

Dr. Segil said he would like to see blood tests to accompany this research to see if participants’ sugars and albumin go up or down.

“I’d love to see these kinds of tests repeated with some blood tests to provide more meaningful data to a physician like myself, to see if these kinds of things change things in the blood,” he added. “And then if it changes things in the blood, the next step would be (to) see if they change things in the brain.”

MNT also spoke with two registered dietician nutritionists for their reaction to this study’s findings.

“Knowing the connection between the gut-brain axis, I was not surprised that the study observed a positive impact on cognitive health markers by way of prebiotic supplementation,” Monique Richard, a registered dietitian nutritionist and owner of Nutrition-In-Sight explained to MNT.

“The metabolic byproducts from microbes as they break down, ferment, and consume food such as fiber — inulin and FOS used in the study — create other compounds which can be anti-inflammatory, protective, and beneficial for other systems in the body,” she said.

“One side effect of decreased inflammation is (a) possible reduction in brain fog, forgetfulness, confusion or lethargy. Gut microbiota can also assist in forming co-factors — specific nutrient helpers — that optimize pathways for neurotransmitter conduction and assist in the chain of events that helps parts of our brain function on all cylinders,” she continued.

“I often encourage my clients to increase their fiber intake for a whole host of reasons such as lowering blood sugar and cholesterol or to support digestion,” Molly Rapozo, registered dietitian nutritionist and senior nutrition and health educator at Pacific Neuroscience Institute in Santa Monica, CA, told MNT. “Since improving cognition is the primary goal of my patient population, this kind of research outcome will be very motivating for them.”

Both Rapozo and Richard said they would be interested to see similar research carried out with whole food sources of prebiotic fiber rather than supplements.

“I would encourage readers to think about fiber as part of a whole food approach, meaning it is just one component of all the nutrients and variety of compounds we need for a healthy gut. Learn what foods are particularly rich in fiber — hint: fruits, vegetables, beans, nuts, seeds, (and) whole grains — that you like and will eat,” Richard said.

How much fiber to eat

“A very general recommendation is to shoot for consuming 25-35 gm of fiber a day. As an example, 1/2 cup of beans can range from 6–9 grams of fiber, depending on the type of bean/pulse.”
— Monique Richard, registered dietitian nutritionist

“Pull up a chart online listing the amounts of fiber in certain foods to gauge how much you may be taking in a day,” she said.

“High-fiber whole foods include additional prebiotic fibers — as the study supplemented with two instead of all four types — as well as antioxidants, vitamins, and minerals,” Rapozo explained.

“The following common vegetables are high in prebiotic fiber: garlic, onion/leek/shallot, asparagus, beets, fennel, green peas, snow peas, corn, and cabbage. Legumes that are a good source of prebiotics are chickpeas, lentils, kidney beans, and soybeans. Fruit sources include apples, nectarines, peaches, persimmon, watermelon, grapefruit, and pomegranate. Whole grains include barley, rye, wheat, and oats. Cashew and pistachio nuts are high in prebiotic fiber as well.”
— Molly Rapozo, registered dietitian nutritionist