Inflammation is central to the pathophysiology of musculoskeletal conditions such as osteoarthritis and rheumatoid arthritis. Nutrition has an influential role in such conditions (Fettke et al, 2023), with insulin attracting particular interest.
Insulin and arthritis
Qiao et al (2020), noted that type 2 diabetes is characterised by insulin resistance – a hyperinsulinaemic state distinguished by a reduced response to the hormone insulin. Hyperinsulinemia is an independent risk factor for osteoarthritis. As fibroblast-like synoviocytes (FLSs) are crucial to the development of synovial inflammation in osteoarthritis, Qiao et al (2020) investigated the role of insulin in relation to FLSs in osteoarthritis. They found that proinflammatory cytokine production in FLSs was raised after insulin stimulation. The discovery that insulin can promote synovial inflammation in the progression of osteoarthritis, either alone or with inflammatory factors, is significant in terms of shaping dietary approaches to such conditions.
Metabolic syndrome
Metabolic syndrome is defined as central obesity as assessed by waist circumference, plus any two of raised tryglyceride concentrations, reduced high-density lipoprotein cholesterol concentrations, hypertension, or hyperglycaemia. Hussain et al (2014) conducted a study of 660 participants with osteoarthritis of the knee and 562 with osteoarthritis of the hip. Metabolic syndrome was associated with an increased incidence of severe knee osteoarthritis requiring total knee replacement. They concluded that management of metabolic syndrome may reduce the burden of knee osteoarthritis.
Impact of diet
To what extent can dietary choices influence symptoms such as pain? Schönenberger et al (2021) undertook a systematic review and meta-analysis of 12 studies to investigate how potentially anti-inflammatory diets (Mediterranean, vegetarian, vegan, ketogenic) compared with an ordinary omnivorous diet influenced pain in adults with rheumatoid arthritis. Although the studies had a high risk of bias and low-quality evidence, they found:
‘The main conclusion is that anti-inflammatory diets resulted in significantly lower pain than ordinary diets.’
Insulin resistance, metabolic syndrome, and diabetes are associated with higher rates and poorer outcomes among those with rheumatoid arthritis. Therefore, Fettke et al (2023) suggested that the benefits of a ketogenic diet – typically less than 50 g of total dietary carbohydrate per day – could be a promising supportive therapy, citing experimental data to support anecdotal claims. In this context, it is interesting to consider the findings of a mini review by Ciaffi et al (2021). They suggested not only that the clinical effect of a ketogenic diet may in the first instance be attributed to an improvement in insulin sensitivity, but that the fat loss and weight reduction as a result of undertaking a ketogenic diet account for part of the anti-inflammatory effects and for the impact of a ketogenic diet on cardiovascular health.
Intriguingly, Ciaffi et al (2021) observed:
‘In rheumatoid arthritis, fasting was shown to be effective in reducing disease symptoms, possibly through the production of β-hydroxybutyrate, the main ketone body.’
Ciaffi et al (2021) noted that during Ramadan – when Muslims refrain from eating and drinking from dawn to sunset – this was effectively a month of intermittent fasting. They stated that one study found non-significant higher disease activity scores before than during Ramadan and a significant improvement in morning stiffness and functional disability during the fasting period.
Given how the musculoskeletal system can be adversely affected by metabolic syndrome, obesity, inflammation and diabetes, Fettke et al (2023) stated that:
‘Low carbohydrate healthy fat lifestyles such as a ketogenic diet show improvement and reversal of these background conditions …’
They suggested that dietary change should be considered as a first-line adjunctive management option.
More research needed
The relationship between arthritis, inflammation, insulin resistance and diet is clear. The relative shortage of randomised controlled studies on dietary options to address chronic conditions points to a need for further research. This would enable current dietary dogmas to be questioned, relevant investigations undertaken, and firm conclusions established. This might help ameliorate – or even reverse – illnesses such as osteoarthritis and rheumatoid arthritis.