As with other neurodegenerative diseases, neurologic and nutritional elements may interact affecting each other in Parkinson's disease (PD). However, the long-term effects of such interactions on prognosis and outcome have not been given much attention and are poorly addressed by current research. Factors contributing to the clinical conditions of patients with PD are not only the basic features of PD, progression of disease, and the therapeutic approach but also fiber and nutrient intakes (in terms of both energy and protein content), fluid and micronutrient balance, and pharmaconutrient interactions (protein and levodopa). During the course of PD nutritional requirements frequently change. Accordingly, both body weight gain and loss may occur and, despite controversy, it seems that both changes in energy expenditure and food intake contribute. Nonmotor symptoms play a significant role and dysphagia may be responsible for the impairment of nutritional status and fluid balance. Constipation, gastroparesis, and gastro-oesophageal reflux significantly affect quality of life. Finally, any micronutrient deficiencies should be taken into account. Nutritional assessments should be performed routinely. Optimization of pharmacologic treatment for both motor and nonmotor symptoms is essential, but nutritional interventions and counseling could and should also be planned with regard to nutritional balance designed to prevent weight loss or gain; optimization of levodopa pharmacokinetics and avoidance of interaction with proteins; improvement in gastrointestinal dysfunction (e.g., dysphagia and constipation); prevention and treatment of nutritional deficiencies (micronutrients or vitamins). A balanced Mediterranean-like dietary regimen should be recommended before the introduction of levodopa; afterward, patients with advanced disease may benefit considerably from protein redistribution and low-protein regimens.