Daily inulin fiber supplement reduces knee osteoarthritis pain in clinical trial

A daily prebiotic fiber supplement reduced pain and improved certain physical measures in people with knee osteoarthritis, according to results from a randomized controlled trial led by researchers at the University of Nottingham.

The INSPIRE trial tested inulin, a natural soluble fiber found in chicory root, Jerusalem artichokes and other vegetables, at a dose of 20 grams per day. Published in the journal Nutrients, the six-week study involved 117 community-dwelling adults with knee osteoarthritis (mean age 67.5 years). Participants were assigned to one of four groups: inulin alone, digital physiotherapy-supported exercise alone, a combination of both, or a maltodextrin placebo (University of Nottingham; Nutrients).

Both inulin and the physiotherapy program independently reduced knee pain compared with placebo. The baseline-adjusted between-group mean difference for pain on the Numerical Rating Scale was −1.11 for inulin and −1.55 for physiotherapy. There was no evidence of a synergistic effect when the two were combined. Inulin uniquely improved grip strength and reduced measures of pain sensitivity, including pressure pain thresholds and temporal summation, which reflect how the nervous system processes pain signals. Physiotherapy improved functional tests such as the timed up-and-go and 30-second sit-to-stand but did not affect grip strength or pain sensitivity in the same way (ScienceDaily; Nutrients).

Retention was markedly higher with the supplement. Only 3.6% of participants in the inulin group dropped out, compared with 21% in the physiotherapy group. Lead author Dr. Afroditi Kouraki of the University of Nottingham School of Medicine noted that the findings suggest targeting gut health with a prebiotic is a safe, well-tolerated approach that people can more easily incorporate into daily routines (University of Nottingham).

Mechanistic data showed that inulin increased circulating levels of the short-chain fatty acid butyrate and the gut hormone glucagon-like peptide-1 (GLP-1). Higher GLP-1 levels were associated with better grip strength, pointing to a possible gut-muscle-pain connection. Inulin acts as a prebiotic that nourishes beneficial gut bacteria, which produce short-chain fatty acids capable of influencing inflammation and pain pathways (News-Medical; Nutrients).

Knee osteoarthritis affects hundreds of millions of people worldwide and is a leading cause of chronic pain and disability, particularly among older adults. Standard approaches often rely on pain medications with potential side effects or exercise programs that many patients find difficult to sustain long-term. Senior author Professor Ana Valdes highlighted the GLP-1 and grip-strength link as warranting further investigation into a broader gut-muscle-pain axis with possible implications for aging and physical resilience (US News/HealthDay).

Professor Lucy Donaldson, Director of Research at Arthritis UK, which supported the work, described the results as preliminary research illustrating how diet and physiotherapy can benefit people with arthritis through different mechanisms. The study was registered on ClinicalTrials.gov (NCT05670314) and followed CONSORT guidelines. Researchers emphasized that while the pain reductions were meaningful, larger and longer trials would help confirm durability and broader applicability (University of Nottingham).

The findings add to emerging evidence connecting the gut microbiome to chronic pain processing and suggest a simple dietary fiber intervention may offer an accessible option alongside established non-pharmacological treatments for knee osteoarthritis.