A Daily Fiber Powder Eased Knee Arthritis Pain, and People's Grip Got Stronger Too

I’ve always filed fiber at the dull end of the supplement aisle, next to the stuff that keeps you regular, so here’s a question I never expected to ask: why would a spoonful of it a day make your hands stronger? In a University of Nottingham trial, older adults with aching knees took 20 grams of a prebiotic fiber called inulin every day for six weeks. Their knee pain eased, which was what the trial set out to achieve. Their grip also got stronger, by 4.62 kilograms over placebo, in a study that was about knees.

The trial, called INSPIRE, was published in Nutrients in February, and it’s been getting a second round of attention since ScienceDaily ran Nottingham’s write-up this week. The researchers randomized 136 adults with knee osteoarthritis into four groups. One took inulin, a fiber found in root vegetables like chicory. One followed Joint Academy, a digital physiotherapy-and-exercise program. One did both, and one took a placebo powder. The 117 people who finished averaged 67.5 years old, 58% were women, and they started at moderate pain, just under 4 on a 10-point scale.

Pain was what the trial was built to measure, and the fiber hit it, though only just. After adjusting for baseline, pain in the inulin group fell 1.11 points more than in the placebo group. The exercise group came in at 1.55, and people doing both landed at 1.67. The authors count a 1-point change as the smallest clinically important difference, and all three average effects sit above it, but the fiber’s barely clears: its 95% confidence interval runs from 2.18 points all the way down to 0.04, with p = 0.045. Adding fiber to exercise produced no measurable synergy, though the trial was too small to detect one if it existed.

Any self-rated pain score comes with a catch, and this one is in the gut. Of the 50 people who finished either inulin arm, 23 reported wind or bloating, and the paper lists no adverse events in the groups that never got inulin. If your belly is bubbling, you can probably guess which powder you were given. The placebo wasn’t dose-matched either: 10 grams of maltodextrin against 20 of inulin, cut in half because of concerns about blood-sugar spikes. An intention-to-treat check that included all 136 people randomized gave consistent results. That helps, but no reanalysis fixes a placebo that people could guess.

That’s why the other measurements are worth a close look. Exercise did what you’d expect: the physiotherapy group got faster at standing up from a chair and at the Timed Up and Go walking test. Inulin moved neither of those and instead showed up where nobody was looking. Grip strength in the inulin group came out 4.62 kilograms ahead of placebo (95% CI 1.67 to 7.57). Inulin also raised pressure pain thresholds at the knee, so it took a harder press to make it hurt, and it dampened temporal summation, the way a repeated poke at one spot hurts more each time as the nervous system winds itself up. Exercise alone showed no effect on grip, pressure threshold or summation. Grip still depends on how hard you’re willing to squeeze, so it isn’t immune to expectation, but it’s a measured performance rather than a number you choose on a 0-to-10 scale.

Wait, why would a gut fiber reach your hands at all? This is where I got hooked. Inulin slides through your stomach and small intestine undigested. In the colon, bacteria ferment it and pour out butyrate, a short-chain fatty acid, and butyrate came out higher in the inulin groups than in the others. GLP-1, the gut hormone whose drug mimics built the Ozempic economy, rose from baseline only in the inulin groups. Within those groups, people with more GLP-1 tended to grip harder (mixed-model β = 0.25, p = 0.006). Senior author Ana Valdes called that link “particularly intriguing” and said it points to “a broader gut–muscle–pain axis” worth chasing. The fine print is worth reading too. The hormone measurements were exploratory, not prespecified. The paper’s wider set of GLP-1 correlations didn’t survive correction for multiple comparisons, and it doesn’t say whether the grip association did. What the data show is GLP-1 and grip rising together, not proof that the hormone did the work, and nothing in the trial connects GLP-1 to the knee pain.

Still, that hormone puts a cheap powder in the same conversation as a very expensive drug. In 2024 the New England Journal of Medicine published STEP 9, Novo Nordisk’s trial of weekly semaglutide in 407 people with obesity and knee osteoarthritis. Over 68 weeks, WOMAC pain fell 41.7 points on the drug versus 27.5 on placebo, along with 13.7% weight loss against 3.2%. Those were different patients on a different pain scale, followed more than ten times as long, so the two trials can’t be lined up. Because the drug’s relief came packaged with heavy weight loss, STEP 9 can’t tell you whether GLP-1 itself does anything for joints. One trial pushed GLP-1 signaling with a patented weekly injection, and the other nudged the body’s own supply with a food-grade fiber. Nobody has tested the two side by side.

The exercise program struggled most on retention. Only 2 of the 55 people assigned to the arms without physiotherapy dropped out, 3.6%, compared with 17 of 81 in the two exercise arms, or 21%. Lead author Afroditi Kouraki said “people were able to fit this supplement easily into their daily lives.” If a physio has ever handed you a home-exercise sheet, you know how that 21% happens.

The money was public and charity money: the Medical Research Council’s Advanced Pain Discovery Platform, Versus Arthritis (now Arthritis UK), UKRI and Nottingham’s NIHR research centre. No company appears among the funders, and the sponsors had no hand in design or analysis. The authors do disclose company ties. Valdes and coauthor Amrita Vijay sit on the scientific advisory board of the nutrition company Chuckling Goat, and Valdes also sits on the advisory board of OLIPOP, the prebiotic soda maker whose refrigerated line lists chicory root inulin and Jerusalem artichoke inulin in its fiber blend. The paper calls those affiliations “not related to this particular study.” That’s worth knowing, but it isn’t evidence that anything went wrong. Arthritis UK, which helped pay for the trial, has its research director, Lucy Donaldson, on record calling it “exciting preliminary research.”

The trial leaves a question that would be cheap to answer: do the grip and pain-sensitivity gains hold over six months, and who actually responds? Inulin is an ordinary food ingredient sold by the tub, not a patented molecule, so that follow-up won’t arrive with a drug company’s budget behind it. It will need the same kind of public and charity money that paid for this one.

If my knees ached, I’d take the trial’s 20 grams a day for its full six weeks, keep doing the exercises, and expect my gut to complain the whole time.

Sources

1. Kouraki et al., Nutrients (2026): Prebiotic supplementation with and without physiotherapy in knee osteoarthritis
2. ScienceDaily: A simple daily fiber supplement reduced arthritis pain and improved strength (2026)
3. Hospital Pharmacy Europe: Inulin reduces pain and pain sensitivity in knee osteoarthritis, trial finds (2026)
4. News-Medical: Prebiotic fiber supplement lowers pain sensitivity in people with knee osteoarthritis (2026)
5. 2 Minute Medicine: Semaglutide reduces weight and pain in obese patients with knee osteoarthritis (STEP 9)
6. OLIPOP: What is OLISMART? Get to know the ingredients in OLIPOP