Knee osteoarthritis is a physical health condition characterised by joint degeneration which can lead to chronic pain, stiffness, and reduced mobility. The symptoms massively reduce quality of life and can cause socioeconomic burden.

Exercise is an effective first-line treatment for knee osteoarthritis pain. While nutrition is a key modifiable factor in chronic pain treatments, evidence for dietary interventions in osteoarthritis remains mixed, highlighting the need to further explore nutritional strategies that may complement established non-pharmacological treatments.

A recent study published in the Open Access journal Nutrients explores the effect of prebiotic fibre supplementation on individuals with knee osteoarthritis. Inulin, a soluble prebiotic fibre, was shown to improve pain sensitivity, an effect not observed with physiotherapy-supported exercise.

Overall, this work reveals a unique perspective to osteoarthritis pain management, underlining the potential for holistic approaches that integrate dietary interventions alongside existing pain management treatments. Dr Afroditi Kouraki, lead author of the study, emphasises the potential clinical implications of this approach:

“This study raises the exciting possibility that a simple dietary change – adding a fibre supplement to your breakfast or yogurt – could meaningfully reduce pain and improve physical function.”

The potential of the gut-microbiome to effect pain

Gut health, which is influenced by prebiotics, plays a crucial role in regulating immune function, inflammatory processes, and neurotransmitter production. Disruptions in the gut microbiota may, therefore, contribute to pain and pain sensitisation through its effects on the gut–brain axis. In particular, microbial metabolites, such as short-chain fatty acids, can modulate neural pathways that are involved in pain perception, potentially influencing pain sensitivity.

Inulin is a soluble prebiotic fibre, found naturally in a variety of plant sources. It has been proven to promote the growth of beneficial bacteria in the gut and enhance the production of bioactive metabolites, such as short chain fatty acids.

Alongside these gut microbiome-related effects, glucagon-like peptide-1 (GLP-1), a hormone produced in the intestine, has emerged as an important signalling molecule of the gut–brain and gut–muscle axes. Dietary fibres enhance the levels of secreted GLP-1, and preclinical studies provide evidence that it may also regulate how the nervous system responds to pain stimuli.

Prebiotics may influence inflammatory and pain pathways, potentially complementing the benefits of exercise. This study evaluated the effects of inulin supplementation, independently and combined with physiotherapy, on knee pain. Measured outcomes included perceived pain perception scores, pressure pain detection thresholds, functional performance (e.g., walking and squatting), and circulating levels of short-chain fatty acids and GLP-1 as potential mechanistic markers.

Comparing the effects of fibre supplementation versus exercise on pain

The study involved 117 participants, over a period of 6 weeks, randomly assigned to 4 groups:

• Group receiving digitally delivered physiotherapy-supported exercise.
• Group receiving inulin supplementation.
• Group receiving inulin supplementation and digitally delivered physiotherapy-supported exercise.
• Group receiving placebo.

Pain reduction

Both exercise and inulin independently led to meaningful reductions in pain compared to the placebo. The group receiving both interventions showed the greatest overall improvement. However, the authors note that the study was underpowered to detect if there was a true synergistic effect between them, likely due to the relatively small sample size.

Physical function

Exercise had a positive effect on functional measures, with participants in this group showing clear improvements in activities such as walking and squatting. Inulin supplementation showed no improvement in these measures.

Interestingly, inulin supplementation was linked to greater improvements in hand grip strength, suggesting it may support different aspects of physical performance.

Effects on pain sensitivity

Notably, there was evidence that fibre effects how the body processes pain. Participants taking inulin, either alone or in combination with physiotherapy, showed improvements in pain pressure threshold, meaning they became less sensitive to pressure at the knee. They also demonstrated reduced temporal summation, indicating a dampening of how the central nervous system amplifies pain signals.

These changes were not observed in the exercise only group, highlighting a potentially unique role for inulin in targeting pain sensitivity.

Explaining the effects of fibre supplementation on pain sensitisation

The authors hypothesised that correlations between short-chain fatty acid levels and pain sensitisation could help explain the effects of inulin supplementation. However, no significant correlations were identified, indicating that the effects of inulin are likely driven by a different mechanism.

As evidence suggests that GLP-1 is influenced by fibre intake and may affect pain processing, its levels were measured to assess changes in response to the interventions. Higher levels were positively associated with grip strength, suggesting that improvements in muscle function may align with GLP-1-related metabolic responses in the inulin groups.

It is important to note that these analyses were exploratory and fell outside the original scope of the study and should therefore be considered preliminary. However, they highlight a potential avenue for future research, as noted by Professor Ana Valdes, co-author of the study:

“The link we observed between GLP-1 and grip strength is particularly intriguing and points to a broader gut–muscle–pain axis that warrants further investigation. This could have implications not just for osteoarthritis, but for understanding how gut health influences ageing and physical resilience more broadly.”

Opening new doors to future studies

The study highlights the potential for both inulin supplementation and exercise to produce clinically meaningful improvements in knee osteoarthritis pain. Notably, the interventions appeared to target different aspects of pain and function. Exercise was more effective in improving functional outcomes, such as walking and squatting ability, whereas inulin supplementation showed greater effects on pain sensitisation indices, suggesting a role in modulating underlying pain mechanisms.

Although prebiotics are thought to influence the gut microbiome through the production of short-chain fatty acids, no association was observed between these metabolites and changes in pain or functional outcomes in this study. Instead, inulin supplementation was associated with increased levels of GLP-1, which in turn correlated with improvements in grip strength. These findings raise further hypotheses regarding the role of GLP-1 in pain modulation and muscle function.

Additionally, substantially lower dropout rates were observed in the inulin group compared to the exercise group (3.6% vs 21%). While the study was not designed to assess long-term adherence, this may suggest that nutritional interventions are more acceptable for some individuals suffering from knee osteoarthritis.

Together, these findings support further investigation into the role of dietary strategies in reducing the burden of osteoarthritis in the general population.

More studies on bone health can be found across the Open Access journals Osteology and Nutrients. Alternatively, you can access the full MDPI journal list here.