A six-week randomized controlled trial run at the University of Nottingham reports that adults with knee osteoarthritis who took a daily prebiotic fiber supplement had significant reductions in pain, improved grip strength, and decreased sensitivity to pain. The results were published in the journal Nutrients.

The fiber in question is inulin, which occurs naturally in chicory root and Jerusalem artichokes. It is classified as a prebiotic rather than a probiotic: digestive enzymes in the small intestine do not break it down, so it reaches the large intestine, where gut bacteria ferment it.

Butyrate, GLP-1 and a gut-muscle link

When bacteria ferment inulin they produce short-chain fatty acids, including butyrate, which the researchers describe as supporting the intestinal lining and influencing inflammation and pain pathways. Participants taking inulin had increased butyrate levels, which the team reads as evidence the supplement was acting on the microbiome.

They also measured higher levels of GLP-1, the gut hormone targeted by drugs such as Ozempic and Wegovy. The supplement is not a GLP-1 medication, and the question being asked here is whether feeding gut bacteria can shift the body's own production of the hormone.

Key results

The INSPIRE trial enrolled 117 adults with knee osteoarthritis across four arms: inulin alone, digitally supported physical therapy alone, both together, and placebo. Inulin and physical therapy each independently reduced knee pain.

What separated them is what came with it. Only the inulin groups showed better grip strength and reduced pain sensitivity, and higher GLP-1 levels were associated with better grip strength, an association the researchers are careful to say does not establish cause.

The dropout gap

The most quietly useful number in the paper is adherence. Dropout was 3.6% in the inulin-only group against 21% in the physical therapy-only group, which lead author Dr. Afroditi Kouraki calls encouraging from a public health perspective.

That gap is the honest argument for this line of research. An intervention people actually keep doing is worth studying even when the effect size is modest.

Limitations

The trial was relatively small and ran only six weeks, and the authors say larger studies with longer follow-up are needed to establish whether the effects persist, who responds, and what the mechanism is.

The researchers also state plainly that fiber supplements are not a replacement for exercise or established arthritis care.

Bottom line

Senior author Professor Ana Valdes points to a broader gut-muscle-pain axis that she says warrants further investigation, with possible implications for aging beyond osteoarthritis. For now it is one short trial, well designed, and unreplicated.