A daily 20-gram dose of inulin, a prebiotic fiber found in chicory root, reduced knee osteoarthritis pain over six weeks by about as much as a digital physiotherapy program, and was the only intervention to improve grip strength and pain sensitivity, in a randomized, placebo-controlled trial led by the University of Nottingham. The peer-reviewed results were published in the journal Nutrients on February 24, 2026, and publicized by the university in March.

The INSPIRE trial enrolled community-dwelling adults with knee osteoarthritis and used a two-by-two factorial design: 136 people were randomized to inulin alone, to physiotherapy-supported exercise (PSE) delivered through a digital program, to both, or to a placebo of 10 grams a day of maltodextrin, according to the paper. Participants had a mean age of 67.5 years, 58 percent were women, and their average pain score at the start was about 4 on a numerical rating scale. A total of 117 completed baseline and follow-up assessments; the 19 who withdrew after baseline were included in an intention-to-treat analysis using multiple imputation.

On the primary outcome, pain on that scale, inulin lowered scores by 1.11 points more than placebo after adjusting for baseline (95% confidence interval, -2.18 to -0.04; p = 0.045), and PSE by 1.55 points (95% CI, -2.52 to -0.58; p = 0.002). Combining the two did not produce an additional benefit, though the authors note the trial was not powered to detect an interaction. A report in Hospital Pharmacy Europe said both improvements exceeded the minimum clinically important difference.

The two treatments worked in different ways. Exercise improved the timed up-and-go test (p = 0.02) and the 30-second sit-to-stand test (p = 0.0004). Inulin improved grip strength (p = 0.002) and two measures of pain sensitivity, pressure pain thresholds (p = 0.009) and temporal summation (p = 0.025). Only inulin raised blood levels of butyrate, a short-chain fatty acid made by gut bacteria, and of the hormone GLP-1, and higher GLP-1 was associated with better grip strength.

Retention differed sharply. Dropout was 3.6 percent in the inulin-only group compared with 21 percent in the physiotherapy groups (p < 0.01). Gastrointestinal side effects from inulin were generally mild and did not lead anyone to stop, according to Hospital Pharmacy Europe.

Dr. Afroditi Kouraki, the lead author, from the University of Nottingham’s School of Medicine, said in the university’s announcement, also distributed through EurekAlert, that the findings suggest “targeting gut health with a prebiotic supplement is a safe, well-tolerated, and effective way to reduce pain.” Senior author Professor Ana Valdes called the link between GLP-1 and grip strength “particularly intriguing” and said it points to a gut-muscle-pain axis that warrants further investigation. Professor Lucy Donaldson, director of research at Arthritis UK, described the work as “exciting preliminary research.”

The trial was funded by the UK Medical Research Council’s Advanced Pain Discovery Platform and by Versus Arthritis. Two of the authors, including Valdes, sit on the scientific advisory board of the nutrition company Chuckling Goat, and Valdes also advises OLIPOP Inc.; the paper states these roles are unrelated to the study and had no role in its design, data handling, writing or publication decision.

Why it matters

Knee osteoarthritis is common and its pain is hard to treat; Donaldson noted in the announcement that six in 10 people with arthritis live in pain most or all of the time. Exercise remains a core treatment, but adherence is a persistent problem, and the trial’s very low dropout in the supplement group suggests a fiber intervention is one that patients can stick with. The authors caution, however, that the results do not suggest fiber should replace exercise or other established treatments.

The mechanism findings add to interest in the gut microbiome’s role in pain. The researchers propose that inulin feeds gut bacteria that produce butyrate, which may influence inflammation and pain pathways, and that GLP-1 may link gut and muscle, though they present these as possible explanations rather than established ones.

The caveats

The trial was small and lasted six weeks, so it cannot say whether the benefit persists, and the authors call for larger, longer studies to confirm the effect and identify who responds. Participants could not be blinded to whether they received physiotherapy, dropout differed between groups, and the GLP-1 analyses were exploratory. The press-release language about a “safe” and “effective” supplement rests on a single trial with 117 completers, and the pain benefit from inulin was modest, just over one point on a numerical scale, with a confidence interval that nearly touched zero. Anyone considering a high-dose fiber supplement for joint pain should discuss it with their doctor.

What to watch

Valdes said the gut-muscle-pain link warrants further investigation, and the authors have called for larger and longer trials; no follow-up study has been announced in the sources reviewed. For now the result remains, in the words of Arthritis UK’s research director, preliminary.

This article is for general information and does not replace advice from a qualified clinician. Corrections: email the editor using the address on the Contact page.