Can a fibre supplement ease knee arthritis pain? What the 2026 Nottingham inulin trial found

Can a daily spoonful of inulin, a soluble fibre found in chicory root, ease knee arthritis pain? The question comes from a University of Nottingham trial published in Nutrients on 24 February 2026. Over six weeks, 117 adults with knee osteoarthritis who completed the trial took 20 g of inulin a day, a digital physiotherapy exercise programme, both, or a placebo powder. Pain fell more with inulin than with placebo, by about one point on a ten-point scale.

Short answer: this is an interesting, carefully reported trial, and inulin is a widely used food ingredient with mostly minor side effects in the trial. It is not proof that a fibre supplement treats osteoarthritis. The pain benefit was small and only just statistically significant, 26 people completed the inulin-only arm, it lasted six weeks, the placebo was a smaller dose of a different powder, and the way people were allocated to groups was changed partway through. Exercise did at least as well for pain in the same trial. NICE names therapeutic exercise and weight management, where appropriate, as core treatments, and the 2019 American College of Rheumatology/Arthritis Foundation guideline strongly recommends exercise among other treatments. If you want to try more fibre, food is the obvious place to start, and a supplement is a reasonable experiment to discuss with a GP or physiotherapist, not a replacement for exercise or prescribed care.

What the Nottingham trial did

The INSPIRE trial (registered as NCT05670314) recruited community-dwelling adults with knee pain from osteoarthritis between May 2022 and February 2025. Of 721 people screened, 136 were randomised, and 117 completed both visits. It used a 2 x 2 factorial design with four groups for six weeks: 20 g a day of inulin powder mixed into cereal, yoghurt, smoothies or a drink; a digital physiotherapy-supported exercise programme delivered through the Joint Academy app; inulin plus the exercise programme; or 10 g a day of maltodextrin, a starch-based powder, as a placebo with usual care. The authors chose the lower maltodextrin dose because of its possible effect on blood sugar. Participants were blinded to inulin or placebo but knew whether they were in an exercise group, and the staff who measured outcomes were blinded to both.

Completers were 58.1% women, with an average age of 67.5 years, an average body mass index of 29.5 and an average starting pain score of 3.96 on the 0 to 10 scale. The main outcome was average pain in the most painful knee over the past week, rated from 0 to 10.

What it found

• Pain (the main outcome): compared with placebo, after adjusting for starting pain, pain fell by 1.11 points more with inulin (95% confidence interval 0.04 to 2.18), 1.55 points more with exercise (0.58 to 2.52) and 1.67 points more with both (0.57 to 2.77).
• The authors say both treatments passed the 1-point threshold usually treated as the smallest change patients notice, with exercise close to the 2-point threshold for feeling much better and inulin at the lower end. The lower end of the inulin confidence interval was 0.04 points, close to no effect.
• No extra benefit from combining inulin and exercise was seen, but the authors note the trial was not powered to detect one.
• Function: exercise improved sit-to-stand and walking test scores; inulin alone did not. Inulin improved grip strength compared with placebo (by 4.62 kg, 95% confidence interval 1.67 to 7.57).
• Pain sensitivity: more people in the inulin groups improved on pressure-pain and pinprick tests, which the authors describe as measures of pain sensitisation. There is no agreed threshold for a meaningful change on these tests.
• Blood markers: butyrate, a short-chain fatty acid made by gut bacteria from fibre, rose in the inulin groups, but did not track changes in pain. GLP-1, a gut hormone, rose with inulin alone. The GLP-1 analysis was added after the trial began and was not in the original protocol, and the authors describe it as hypothesis-generating.
• Side effects and dropout: 23 of the 50 people who completed an inulin group reported very minor digestive effects such as wind and bloating, which did not lead anyone to stop. Dropout was 21% (17 of 81) in the exercise groups and 3.6% (2 of 55) in the groups without exercise.

Why the result needs caution

The authors list several limitations themselves. Because many more people dropped out of the exercise groups, the researchers changed the allocation probabilities during later recruitment to put more people into those groups; the authors say this reduces the strength of causal inference compared with a fully balanced randomised design, although analyses adjusted for recruitment phase gave similar results. The trial lasted only six weeks. Group sizes were small: 26 people completed inulin alone, 24 inulin plus exercise, 40 exercise alone and 27 placebo. The main analysis included only completers, although an analysis of all 136 randomised participants, with missing results estimated statistically, gave results consistent in direction and size. The placebo was 10 g of maltodextrin, not a matched 20 g dose. The authors did not exclude people who already ate a lot of fibre, though fibre intake did not differ between groups.

Funding came from the Advanced Pain Discovery Platform and the Medical Research Council, Versus Arthritis, UKRI and the NIHR Nottingham Biomedical Research Centre, and the paper says the funders had no role in the study. Two authors, including senior author Ana Valdes, sit on the scientific advisory board of the nutrition company Chuckling Goat, and Valdes also sits on advisory boards for OLIPOP; the paper states these are not related to the study.

The earlier evidence

The idea has one earlier trial behind it. A University of Calgary study published in 2024 randomised 54 adults, mostly women, with knee osteoarthritis and obesity to 16 g a day of oligofructose-enriched inulin or a maltodextrin placebo for six months. The prebiotic group did better on timed walking and grip strength tests than the placebo group. The difference in knee pain did not reach statistical significance (p = 0.059), and the authors called for larger trials. Two small trials pointing the same way are a reason for a bigger one, not yet a reason to change care.

Exercise has a far larger evidence base. A 2024 Cochrane review of 139 trials with 12,468 participants found low- to moderate-certainty evidence that exercise probably improves knee osteoarthritis pain, function and quality of life in the short term, while noting that the size of the benefit may be of uncertain clinical importance and that most participants knew which treatment they were getting.

Our view

• This is a promising early signal, not a treatment. One six-week trial with 26 people on inulin alone, a pain benefit close to the edge of significance and a changed allocation scheme does not settle whether fibre helps knee pain.
• Exercise and, where relevant, weight loss remain the core treatments. In this trial, exercise did at least as well as inulin for pain and better on walking and sit-to-stand tests. Inulin improved grip strength, which the trial also measured.
• In this trial, inulin's digestive effects were described as very minor, and 23 of 50 people who finished an inulin group had wind and bloating at 20 g a day. People with irritable bowel syndrome were excluded from the trial, so it says nothing about them.
• More fibre from food, such as wholegrains, beans, lentils, vegetables, fruit, nuts and seeds, is a good idea for general health whatever happens with this research.
• Do not stop prescribed pain relief or skip physiotherapy because of this trial. Talk to a GP, pharmacist or physiotherapist before adding a supplement, especially if you take other medicines.

UK advice

NICE says the core treatments for osteoarthritis are therapeutic exercise and weight management where appropriate, along with information and support, and that people living with overweight or obesity should be told that weight loss will improve quality of life and physical function, and reduce pain. NICE advises against offering glucosamine, saying there is no strong evidence of benefit. The NHS says adults should aim for 30 g of fibre a day, and that adults eat an average of about 20 g. Fibre supplements are sold as foods or food supplements, with guidance from the Food Standards Agency.

FAQ

What is inulin?

Inulin is a soluble prebiotic fibre found naturally in chicory root, Jerusalem artichoke and other plants. Gut bacteria ferment it, producing short-chain fatty acids such as butyrate. It is sold as a powder and is also added to some foods.

How much inulin did the trial use?

Participants took 20 g of inulin powder a day for six weeks, mixed into food or a drink. The placebo group took 10 g a day of maltodextrin.

Does a fibre supplement treat osteoarthritis?

These trials do not show that. The Nottingham trial measured pain and function over six weeks, not joint damage, and one earlier trial found no statistically significant change in knee pain. Treat the result as a reason for larger trials.