Dietary influences on the antiparkinsonian response to levodopa.

The ability of dietary factors to modify the response to levodopa was evaluated in six patients with idiopathic Parkinson's disease who manifested fluctuations in motor performance. The single oral administration of a high-protein formula substantially elevated plasma large neutral amino acid levels, and prematurely terminated the antiparkinsonian response to levodopa/carbidopa. In contrast, during oral or intravenous administration of levodopa, the ingestion of diets meeting the recommended daily allowance (RDA) for protein had no significant effect on plasma levodopa or large neutral amino acid levels or variance, nor on parkinsonian scores or variance. The results suggest that while protein intake in excess of the RDA can diminish the antiparkinsonian response to orally administered levodopa/carbidopa in patients with advanced disease, diets adhering to RDA protein guidelines have no clinically appreciable effect.