Objective: This study aimed to determine the correlation of glycemic load (GL) and glycemic index (GI) with Parkinson’s disease (PD) in terms of the serum levels of methylglyoxal (MGO), oligomeric α-synuclein (α-syn), and DJ-1. Methods: In this case-control study (40 PD and 40 healthy individuals) dietary intake of the participants was assessed for a 4-day period (24-hour dietary recall questionnaire and three-day food record). Serum levels of MGO, oligomeric α-syn, and DJ-1 were measured by ELISA. Adjusted odds ratios (ORs) for PD were estimated according to quantiles of dietary factors and serum factors. Results: Serum levels of oligomeric α-syn (p = 0.003) and DJ-1 (p < 0.001) were significantly higher in the patients compared to the healthy participants. The participants with PD had higher GI levels (p = 0.02) compared to healthy individuals. A positive correlation emerged between the risks of PD and GI (OR: 10.05; [95%CI: 1.94, 51.95] for the highest vs. the lowest quintile, p for trend 0·028). In the patients, level of GI, but not GL, correlated with MGO [β (95% CI): 0.27 (0.02, 1.98); p = 0.04], oligomeric α-syn [β (95% CI): 0.34 (0.01, 0.17); p = 0.03], and DJ-1 [β (95% CI):0.39 (0.04, 0.30); p = 0.01] positively and significantly. Moreover, serum levels of MGO, oligomeric α-syn, and DJ-1 were associated with each other significantly and positively (p < 0.05). Conclusions: It can be concluded that high GI diets are positively correlated with PD, more possibly by the increased α-syn oligomerization and advanced glycated end products (AGEs) formation.