A Common Fiber Supplement Was Linked to Less Arthritis Pain in Six Weeks

Could the gut help ease knee pain? A familiar dietary fiber is drawing new attention in the search for relief from stubborn joint problems.

A daily fiber supplement achieved what six weeks of physiotherapy did not: it improved handgrip strength in people with knee arthritis. It also eased knee pain and altered how participants reacted to painful sensations, suggesting a possible link between the gut and the joints.

In a six-week clinical trial, researchers at the University of Nottingham examined whether a prebiotic fiber called inulin could help people with knee osteoarthritis. The supplement reduced pain, but its effects differed from those of physiotherapy in ways that drew the team’s interest.

Managing knee arthritis involves more than building strength around the joint. In some cases, something as simple as a supplement taken through the digestive system may affect muscle power and pain sensitivity.

“This exciting preliminary research highlights how diet and physiotherapy can act in different ways to have benefits for people with arthritis,” said Lucy Donaldson, director of research at Arthritis UK, who wasn’t involved in the trial study.

Why scientists looked beyond the knee for arthritis relief

Knee osteoarthritis develops when cartilage and other tissues inside the joint gradually break down. Cartilage normally cushions the ends of bones so they can move smoothly against each other.

As those tissues deteriorate, people can experience ongoing pain, stiffness, swelling, and difficulty walking or climbing stairs.

Exercise and physical therapy can strengthen the muscles that support the knee and help preserve mobility. But sticking with an exercise program is difficult when movement itself hurts. Painkillers may help, but they also bring drawbacks.

In addition, the amount of arthritis pain does not always match the visible damage in the joint, because the nervous system also shapes how pain is experienced.

That has pushed researchers to examine the gut microbiome, the large community of microorganisms in the digestive system. These microbes help regulate inflammation and produce compounds that can affect pain.

The Nottingham team wanted to know whether changing gut bacteria activity could offer another way to manage osteoarthritis symptoms.

Testing 20 grams of fiber

The researchers ran a randomized controlled trial known as INSPIRE. Of the 136 adults with knee osteoarthritis who were randomized, 117 finished the six-week study. The average age was about 68, and 58 percent were women.

Participants were split into four groups. One group received 20 grams of inulin each day, another followed a digitally supported physiotherapy exercise program, a third received both treatments, and the fourth took maltodextrin, a starch used as a placebo.

Inulin is a naturally occurring dietary fiber found in foods such as chicory root, Jerusalem artichokes, onions, and garlic. Unlike digestible carbohydrates, it passes through the small intestine largely unchanged. In the large intestine, beneficial bacteria ferment it and produce short-chain fatty acids.

One of those compounds, butyrate, helps maintain the intestinal lining and may influence inflammation and biological pathways involved in pain. That is why inulin is considered a prebiotic: it feeds the bacteria already living in the gut rather than adding new ones.

Over the six weeks, the team measured knee pain, sensitivity to painful pressure, grip strength, and physical performance, including the ability to rise from a chair and move around.

They also checked biological markers, including short-chain fatty acids and a gut hormone called glucagon-like peptide-1 (GLP-1).

Fiber and physiotherapy helped in different ways

Both inulin and physiotherapy reduced knee pain. Compared with placebo, inulin was linked to a 1.11-point drop in pain on a 10-point scale, while physiotherapy produced a 1.55-point reduction. Both results were statistically significant, although the study did not show that one treatment was better than the other.

Inulin also increased grip strength by an average of 4.62 kilograms compared with placebo and reduced sensitivity to pressure and repeated painful stimulation, benefits not seen with physiotherapy alone.

“This study raises the exciting possibility that a simple dietary change — adding a fiber supplement to your breakfast or yogurt — could meaningfully reduce pain and improve physical function,” Afroditi Kouraki, lead researcher and a research fellow, said.

Physiotherapy, meanwhile, improved performance in tests that measured how quickly participants could stand, walk, and sit down, as well as how many times they could rise from a chair in 30 seconds. Inulin did not produce those gains.

The combination of the two approaches also reduced pain, but the researchers could not determine whether using both together offered an added benefit.

Another difference appeared in adherence. Only 3.6 percent of participants in groups without physiotherapy dropped out, compared with 21 percent of those assigned to groups that included physiotherapy.

For some patients, taking a daily supplement may be easier to sustain than following a structured exercise plan.

“Our findings suggest that targeting gut health with a prebiotic supplement is a safe, well-tolerated, and effective way to reduce pain in people with knee osteoarthritis. The very low dropout rate compared to the exercise group is also encouraging from a public health perspective — people were able to fit this supplement easily into their daily lives,” Kouraki added.

A gut hormone offers an unexpected clue

Participants who took inulin showed higher levels of butyrate and GLP-1, a hormone produced in the gut that helps regulate blood sugar and appetite.

GLP-1 is widely known because diabetes and weight-loss medications such as Ozempic and Wegovy act on its pathway. Inulin itself is not a GLP-1 drug, but it may affect the body’s natural hormone production by changing gut microbial activity.

The researchers found an association between higher GLP-1 levels and better grip strength, pointing to a possible connection between gut bacteria, hormone signaling, and muscle performance.

“The link we observed between GLP-1 and grip strength is particularly intriguing and points to a broader gut-muscle-pain axis that warrants further investigation. This could have implications not just for osteoarthritis, but for understanding how gut health influences aging and physical resilience more broadly,” Ana Valdes, one of the study authors and a professor of Molecular and Genetic Epidemiology, said.

Could fiber become another tool against arthritis pain?

Overall, fiber may be a relatively inexpensive and accessible addition to current arthritis treatments.

Still, the trial was small and lasted only six weeks. It remains unclear whether the benefits last over time, which patients benefit most, or exactly how gut bacteria affect pain and muscle strength.

Although inulin was generally well tolerated, 23 of the 50 participants who completed an inulin-containing treatment reported mild digestive issues, including gas and bloating. None of these symptoms caused anyone to withdraw.

Because more participants dropped out of the physiotherapy groups, the researchers changed how new participants were assigned, adding some uncertainty to the results.

Larger and longer studies will be needed to confirm the findings and determine whether changes in butyrate and GLP-1 are truly driving the improvements.

The study was published in the journal Nutrients.