It has been largely demonstrated that amino acids (AA's) represent a useful nutritional approach to guarantee a correct functioning of the main endogenous antioxidant systems, such as glutathione system. However, such nutritional intervention is not commonly utilised for PD patients because of negative interactions between dietary amino acids and L-dopa pharmacokinetics (the movement of a drug/medication into, through, and out of the body). In accordance with these observations, dietary regimes that shift protein intake to the evening and restrict daily protein intake have been proposed to increase the efficacy of L-dopa which is normally taken 30-60 minutes before meals. Indeed, protein intake reduction during the first part of the day along with a strict control of the total protein amount to the recommended daily allowance is associated with a reduction in both postprandial (after food) and total off time (when PD patients feel as though medication has warn off) in fluctuating PD patients.
However, on the other hand, a long lasting low protein regime raises the question of potential detrimental effects on protein energy balance in a population with an intrinsic tendency toward chronic protein malnutrition. It is believed that long-lasting PD affected patients display a higher risk of developing malnutrition and sarcopenia (loss of skeletal muscle mass and strength). The estimated overall prevalence with the Parkinson's population group stands at approximately 24 percent. Moreover, the risk of developing malnutrition increases with the disease progression. Causes of malnutrition in PD are various: motor disability, with mastication and deglutition difficulties, especially in an advanced stage, together with some non-motor symptoms such as anxiety, depression and apathy - leading to a reduction in caloric intake.
In a recent study (In Press, 2015) researchers from the University of Udine and Trieste, Italy, evaluated the effects of AA supplementation on a PD patients nutritional status and motor performance, as well as on the pharmacological control of the disease. Specifically, the researchers investigated the effect of 6 months of AA supplementation in protein restricted PD patients, chronically treated with L-dopa, to identify whether intervention had an impact on fluctuations in a PD patients therapeutic response. The results of the preliminary data from this study indicate that AA supplementation has no detrimental effects in L-dopa chronically treated patients, improves both insulin sensitivity (insulin resistance can develop in PD patients due to dopaminergic degeneration) and oxidative status (low antioxidant status has been associated with both the aetiology and progression of PD). Nonetheless, amino acid supplementation failed to improve "off time" or significantly increase motor ability.
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