The effect of diet on Parkinson's disease progression, symptoms and severity: a review of randomised controlled trials.

Parkinson's disease (PD) is the fastest-growing neurological condition in the world, affecting 11·8 million people worldwide in 2021. Due to the globally expanding and ageing population, as well as growing industrialisation, this number is likely to increase. Given the absence of disease-modifying pharmacological therapies, this review aimed to examine the effect of dietary interventions on PD progression, motor symptoms, non-motor symptoms, specifically those affecting the gastrointestinal (GI) tract, and severity. To do so, this review synthesised the current evidence from randomised controlled trials (RCTs) on dietary patterns, individual foods and beverages, and nutritional supplements including nutrients, bioactive compounds, and biotics.Results from the included RCTs failed to demonstrate conclusive evidence for the use of a dietary intervention as a therapy for improving PD progression, symptoms and severity. However, this is likely a reflection of the current scarcity of RCTs in the literature, rather than an outright demonstration of the ineffectiveness of such dietary approaches. In contrast, several trials have demonstrated a beneficial effect of biotic supplementation in managing GI symptoms, particularly constipation syndrome, which may be a promising avenue for improving GI-related issues that affect up to 80 % of PD patients. In conclusion, further RCTs are required to decipher the role that diet may play in mitigating PD progression and severity and improving overall patient care by reducing both motor and non-motor symptoms.