Weight changes and physical activity in Parkinson's disease: converging markers of energy balance, disease progression, and lifestyle-based care.

Weight changes are common but often overlooked in Parkinson's disease (PD), occurring across prodromal, early, and advanced disease stages. Weight loss may reflect increased energy expenditure, dysautonomia, dysphagia, gastrointestinal dysfunction, altered appetite, and involvement of central pathways regulating hunger, satiety, and reward. Conversely, weight gain may occur in relation to dopaminergic treatment, impulse-control or binge-eating behaviours, reduced mobility, and post-surgical changes. Emerging longitudinal data suggest that weight variability is not merely a nutritional issue, but may identify distinct clinical trajectories, including faster cognitive and functional decline in patients with weight loss and different motor/non-motor patterns in those with weight gain. In parallel, physical activity and structured exercise are increasingly recognized as central components of PD care, with evidence supporting symptomatic benefits, possible disease-modifying effects, and even a protective association against incident PD. This review examines the intersection between weight changes and physical activity in PD, proposing that both reflect a broader disruption of energy balance, motor reserve, metabolic regulation, and lifestyle-related resilience. We discuss clinical mechanisms, biomarkers, prognostic implications, and practical approaches to integrate weight monitoring, nutritional assessment, and individualized physical activity prescriptions into routine PD care.