A Daily Fiber Supplement May Ease Knee Arthritis Pain and Build Grip Strength, Trial Finds

In a six-week trial of 117 adults with knee osteoarthritis, the group taking a daily inulin supplement reported less knee pain, and almost all of them stayed with the program to the end. Only 3.6% of people assigned to inulin alone dropped out. Among those assigned to digitally supported physical therapy alone, the figure was 21%.

The study, called INSPIRE, was a randomized controlled trial published in the journal Nutrients. Participants were placed in one of four groups: inulin alone, physical therapy exercises alone, inulin combined with physical therapy, or a placebo. That setup let the researchers look at each approach separately and ask whether combining them added anything.

Inulin is a naturally occurring fiber found in chicory root, Jerusalem artichokes and certain other vegetables. Digestive enzymes in the small intestine do not break it down. It travels to the large intestine, where gut bacteria use it as food, which is why it is classed as a prebiotic. Probiotics, by contrast, supply living microorganisms directly.

Both inulin and physical therapy reduced knee pain on their own. But the supplement produced further changes that physical therapy alone did not. People taking inulin had better grip strength and reduced pain sensitivity, meaning their nervous systems responded less strongly to potentially painful stimulation. That matters in osteoarthritis because persistent pain is not always explained by how much visible damage a joint has sustained; how the nervous system processes pain can contribute too.

The researchers also looked at what was happening in the gut. When bacteria ferment inulin, they produce short-chain fatty acids, among them butyrate, which supports the intestinal lining and can influence inflammation and pain-related pathways. Participants taking inulin had higher butyrate levels. They also had higher levels of glucagon-like peptide-1, or GLP-1, a gut hormone involved in regulating blood sugar and appetite, and linked to pain regulation and muscle health. GLP-1 is the hormone targeted by drugs such as Ozempic and Wegovy, but the inulin here was not a drug of that kind; the question was whether feeding gut bacteria could influence the body's own production of it. Higher GLP-1 was associated with better grip strength, though the study does not show that GLP-1 caused the improvement.

Dr. Afroditi Kouraki, lead author from the University of Nottingham's School of Medicine, said the results raise the possibility that adding a fiber supplement to breakfast or yogurt could meaningfully reduce pain and improve physical function. She described the approach as safe, well tolerated and effective, and called the low dropout rate encouraging from a public health standpoint. Senior author Professor Ana Valdes called the GLP-1 and grip strength link intriguing, pointing to a broader gut-muscle-pain axis that could matter for aging and physical resilience beyond osteoarthritis.

The caveats are plain. The trial was small and lasted only six weeks. Larger studies with longer follow-up are needed to learn whether the benefits last, which patients respond best, and how the biology works. The results do not suggest fiber should replace exercise or established treatments, only that it might complement them.

The condition itself affects hundreds of millions of people worldwide, causing pain, stiffness, swelling and trouble with walking or climbing stairs, especially in older adults. Professor Lucy Donaldson, Director of Research at Arthritis UK, noted that a survey of people with lived experience found six in ten are in pain most or all of the time. She called the work exciting but preliminary, showing that diet and physiotherapy may act in different ways. The next step is larger, longer trials.