This is a Phase IIa, randomized, double-blinded, placebo-controlled trial to determine the tolerability of L-serine for Mild Cognitive Impairment patients and assess preliminary indications of efficacy. Efficacy will be assessed by cognitive testing, FDG-PET scans and biomarkers in plasma. Up to 125 subjects will be enrolled, with the aim of having 100 subjects complete the trial. Subjects participating in the study will be randomized to receive either jellybeans containing L-serine or placebo jellybeans, with the Investigator, study staff and patients and Sponsor blinded to the individual patient assignments. An individual subject’s participation in the study will last 6 months from time of enrollment, with blood draws and cognitive assessments made at the beginning, 3-months and end of the 6-month treatment period.