This is a prospective, double-blind, randomized control trial with a repeated measures design. After being screened via phone screens and completing an initial visit that includes additional in person screening and the collection of descriptive information, participants will be invited to take part in three experimental sessions. On three separate days participants with idiopathic Parkinson's Disease and taking a stable dose of dopamine replacement medication, 2-3 hours after a standardized low-protein meal, will orally take a habitual dose of L-Dopa medication and then engage in one of the three interventions 1) WP-S: whey protein supplement (20 g), 2) AA-S: targeted amino acid supplement (equivalent amino acid load to whey protein beverage) 3) CON-S: an isonitrogenous placebo beverage (equivalent amino acid load to whey protein beverage), prescribed in a randomized and counterbalanced manner. Prior to, and up to 3 hours after medication, blood samples will be collected every 15 min for 90 min and every 30 min thereafter and then analyzed to determine circulating L-dopa and amino acid profiles using high-performance liquid chromatography. During this observation period changes in both motor (Movement Disorder Society-Unified Parkinson's Disease Rating Scale Part 3 (MDSUPDRS III), finger tapping, and Timed Up and Go Test) and non-motor disease symptoms (Profile of Mood State with component analysis of depression, fatigue, and anxiety) will be measured every 30 minutes.
All supplements will be provided for the study in coded prepackaged envelopes by an independent nutritional supplement company based on the formulas provided below, to ensure double blinding.
Whey Protein Supplement (WP-S): Whey protein is one of the primary proteins found in all dairy products. It is a complete protein as it contains all the essential amino acids. A previous investigation has been performed looking at the long -term (6 months) effects of whey protein supplementation on health and disease symptoms of people with Parkinson's Disease. This study validated the safety and efficacy of whey protein supplementation in people with Parkinson's Disease, but a non-significant increase in disease symptoms (during medication off time) was reported. Similar to this previous study, we will use a standard 20 g dose of whey protein.
Targeted Amino Acid Supplement (AA-S): Previous studies have investigated the long-term (6 months) effects of amino acid supplementation on health and disease symptoms of people with Parkinson's Disease. The previous whey protein study, and the previous amino acid supplement study, validated the safety and efficacy of an amino acid supplement in people with Parkinson's Disease but a non-significant increase in disease symptoms (during medication off time) was reported. However, the supplement in these studies was not designed to minimize the components which could interfere with levodopa medication.
In contrast, the AA-S used in the present study was designed off the amino acid composition of WP-S, but then was modified to minimize interference with levodopa by reducing the quantity of amino acids which are known to interfere with levodopa (large neutral amino acids), which collectively resulted in a 59% reduction in competing amino acids. Additionally, the concentrations of other non-competing amino acids were modified in order to fill the previously identified nutritional deficiency observed in people with PD.
Isonitrogenous Placebo Supplement (CON-S): The control supplement used in this study is an isonitrogenous placebo beverage. This supplement will consist of an inert amino acid (alanine) with the same amino acid load as the WP-S and AA-S (16.2 g).
