This Simple Fiber Supplement Reduced Arthritis Pain in Just 6 Weeks

Can our gut heal our knees? A familiar dietary fiber is opening a new line of inquiry into one of the most stubborn forms of joint pain.

A daily dose of dietary fiber did something that six weeks of physiotherapy couldn’t. It improved handgrip strength in people with knee arthritis. It also eased knee pain and changed how participants responded to painful sensations, hinting at a strange connection between our gut and joints.

In a six-week clinical trial, researchers at the University of Nottingham tested 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 caught the researchers’ attention.

Managing knee arthritis involves more than strengthening the muscles around the joint. Sometimes, a simple supplement consumed through the digestive system could affect muscle strength 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 within the joint gradually break down. Cartilage normally cushions the ends of bones, allowing them to move smoothly against each other. 

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

Exercise and physical therapy help strengthen the muscles supporting the knee and maintain mobility. However, following an exercise routine can be challenging when movement itself is painful. Painkillers, despite the relief, come with their own problems.

Moreover, the severity of arthritis pain does not always match the amount of damage visible in the joint because the nervous system also influences how strongly people experience pain.

This has encouraged researchers to investigate the gut microbiome, the vast community of microorganisms living in our digestive system. These microbes help regulate inflammation and produce chemicals that can influence pain.

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The Nottingham researchers particularly wanted to know whether changing the activity of gut bacteria could offer another way to manage osteoarthritis symptoms.

Putting 20 grams of fiber to the test

The team conducted a randomized controlled trial called INSPIRE. Of the 136 adults with knee osteoarthritis who were randomized, 117 completed the six-week trial. Participants had an average age of approximately 68 years, and 58 percent were women.

The researchers divided them into four groups. One received 20 grams of inulin daily, 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 ordinary digestible carbohydrates, inulin passes through the small intestine largely intact. When it reaches the large intestine, beneficial bacteria ferment it, producing compounds called short-chain fatty acids.

One of these compounds, butyrate, helps maintain the intestinal lining and can influence inflammation and biological pathways involved in pain. This makes inulin a prebiotic. Rather than introducing new bacteria into the digestive system, it provides food for bacteria already living there.

Over six weeks, the researchers assessed participants’ knee pain, sensitivity to painful pressure, grip strength, and physical performance, including their ability to rise from a chair and move around.

They also examined 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. For instance, compared with placebo, inulin was associated with a 1.11-point reduction in pain on a 10-point scale, while physiotherapy produced a 1.55-point reduction. Both differences were statistically significant, although the study did not establish that one treatment was superior.

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However, inulin also improved grip strength by an average of 4.62 kilograms compared with placebo and reduced sensitivity to pressure and repeated painful stimulation, benefits not observed 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 measuring how quickly participants could stand, walk, and sit down, and how many times they could rise from a chair in 30 seconds. Inulin did not produce these improvements.

The combination also reduced pain, but researchers could not establish whether using both treatments together offered an extra benefit.

Another difference emerged in treatment adherence. Only 3.6 percent of participants in groups without physiotherapy dropped out, compared with 21 percent of those assigned to groups involving physiotherapy.

Taking a daily supplement may be easier for some patients to maintain than following a structured exercise program.

“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 gives an unexpected clue

Participants receiving inulin showed increased 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 biological pathway. However, inulin is not a GLP-1 drug. Instead, it may influence the body’s natural hormone production through changes in gut microbial activity.

The researchers found an association between higher GLP-1 levels and better grip strength, suggesting 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 could be a relatively inexpensive and accessible addition to existing arthritis treatments.

However, the trial was relatively small and lasted only six weeks. It remains unclear whether the improvements persist over time, which patients benefit most, or precisely how gut bacteria influence pain and muscle strength.

Although inulin was generally well tolerated, 23 of the 50 participants who completed an inulin-containing treatment reported minor digestive problems, including gas and bloating. These symptoms did not cause anyone to withdraw.

Since more participants dropped out of the physiotherapy groups, the researchers changed how new participants were assigned, introducing some uncertainty into the results.

Larger, longer trials will be needed to confirm the benefits and determine whether changes in butyrate and GLP-1 actually drive the improvements.

The study is published in the journal Nutrients.