For many people with knee osteoarthritis, everyday activities such as climbing the stairs, getting out of a chair or going for a walk can become increasingly painful.

Current NHS treatment focuses on staying active, strengthening the muscles around the joint, maintaining a healthy weight where appropriate, and using pain relief when needed.

Exercise remains one of the most effective treatments, although many people understandably find it difficult to keep up when their knees are painful.³⁻⁵

Now, a new clinical trial from the University of Nottingham suggests improving gut health may also have a role to play.

Researchers found that taking a daily prebiotic fibre called inulin reduced knee pain, improved pain sensitivity and increased grip strength in adults with knee osteoarthritis over six weeks.¹²

What is knee osteoarthritis?

Osteoarthritis is the UK’s most common form of arthritis.

It develops when the protective cartilage covering the ends of bones gradually wears down, causing joints to become painful and stiff.

The knees are among the joints most commonly affected.

According to the NHS, common symptoms include:

• Pain when moving the joint

• Stiffness, particularly after resting

• Reduced mobility

• Swelling or tenderness around the joint

Although osteoarthritis cannot currently be cured, many people successfully manage their symptoms through lifestyle measures and appropriate treatment.³

What did the researchers investigate?

Scientists at the University of Nottingham wanted to explore whether improving gut health could influence knee osteoarthritis symptoms.

Previous research has suggested that the gut microbiome may play a role in inflammation, pain perception and muscle function.

To investigate this, the researchers carried out a six-week randomised, placebo-controlled clinical trial, one of the strongest ways of testing whether an intervention genuinely works.¹

A total of 136 participants were randomly assigned to one of four groups:

• Inulin (20 g per day, taken as two 10 g servings)

• A digital physiotherapy-supported exercise programme

• Both inulin and exercise

• Placebo (maltodextrin powder)

The inulin dose used in this study (20 g per day) is substantially more than most people would typically consume through food alone.

Of those enrolled, 117 participants completed both the baseline and follow-up assessments, which formed the main analysis.¹

The researchers assessed knee pain, physical function, grip strength, pain sensitivity, blood markers and changes in the gut microbiome.¹

What is inulin?

Inulin is a natural soluble fibre found in foods including:

• Chicory root

• Jerusalem artichokes

• Garlic

• Onions

• Leeks

• Asparagus

Unlike most carbohydrates, inulin passes through the small intestine largely undigested before reaching the large intestine, where it acts as a prebiotic, feeding beneficial gut bacteria.

As these bacteria ferment inulin, they produce compounds known as short-chain fatty acids, which are thought to influence many aspects of health, including metabolism and immune function.

What did the study find?

After six weeks, the researchers found that people taking inulin experienced:

• Reduced knee pain

• Reduced pain sensitivity

• Improved grip strength¹

The digital physiotherapy programme improved measures of physical function, including the Timed Up and Go test and the 30-second sit-to-stand test.¹

People taking inulin also had higher levels of the naturally occurring gut hormone GLP-1. Higher GLP-1 levels were associated with improvements in grip strength, suggesting one possible way that changes in the gut may influence muscle function and pain.¹

The researchers also observed changes in the gut microbiome and increased production of butyrate, a short-chain fatty acid produced when beneficial gut bacteria ferment fibre.

Butyrate has previously been linked with reduced inflammation and healthier gut function, although its exact role in osteoarthritis remains an active area of research.¹

One unexpected finding was that combining inulin and exercise did not produce greater improvements than either intervention alone. The researchers suggest the two interventions may work through different biological pathways, but larger studies are needed to better understand these findings.¹

Does this mean inulin treats arthritis?

No.

This was a relatively small clinical trial lasting six weeks.

While the findings are encouraging, they do not show that inulin treats osteoarthritis or replaces established treatments.

The researchers themselves conclude that larger and longer-term studies are now needed to confirm these findings and better understand how changes in the gut microbiome may influence joint health.¹

What does the NHS recommend?

Current NHS and NICE guidance continues to recommend:

• Regular physical activity

• Muscle-strengthening exercises

• Maintaining a healthy weight where appropriate

• Appropriate pain relief when needed

• Physiotherapy where appropriate³⁻⁵

  
  

Exercise remains one of the most effective treatments for osteoarthritis, even though symptoms can sometimes feel worse when first starting.

Regular activity helps reduce pain and improve function over time.⁴⁻⁵

The new Nottingham research doesn’t replace these recommendations.

Instead, it suggests that improving gut health may eventually become another useful tool alongside them, but further research is needed before any changes to clinical practice can be recommended.¹

Our thoughts

One of the most interesting aspects of this study isn’t simply that knee pain improved.

It’s the possible mechanism behind it.

People taking inulin had higher levels of the naturally occurring gut hormone GLP-1, and those with higher GLP-1 levels also tended to have greater improvements in grip strength.

This points towards what researchers describe as a possible gut-muscle-pain axis — the idea that signals from the gut may influence not only digestion, but also muscle function and how pain is processed elsewhere in the body.

It’s important to remember that this was an association rather than proof that GLP-1 caused the improvements. The researchers themselves describe these findings as exploratory and say further studies are needed to confirm the relationship.

Even so, it’s an interesting result. GLP-1 is best known for its role in regulating blood sugar and appetite, and as the hormone targeted by newer weight-loss medicines. Its possible role in muscle strength and joint pain is only just beginning to be explored.

While it’s still early days, this study suggests the story may be about more than simply increasing fibre intake. It highlights a potential gut-hormone pathway that could eventually help researchers better understand the links between gut health, muscle function and pain.