The Gut - PRO Study

40 participants will be enrolled. 20 with dementia or mild cognitive impairment (MCI) due to Alzheimer's disease (biomarker confirmed amyloid positivity), and 20 unimpaired cognition, enriched for elevated amyloid (approximately 75-80% amyloid positive). Dementia/mild cognitive impairment will be determined according to 2024 NIA-AA criteria. Primary Objective * To assess the safety and feasibility (recruitment, eligibility, enrollment, completion, and follow-up) of an oral probiotic supplementation (PS) intervention in humans with or at risk for dementia due to AD. Exploratory Objectives * To demonstrate the effects of PS on the composition and function of the gut microbiota in humans with or at risk for dementia due to AD. * To collect preliminary data in order to estimate sample size and other critical parameters for a larger study. * To examine potential mechanisms by which the gut impacts brain, including leading candidate mechanisms such as intestinal permeability and change to bile acid milieu.