Miller, Brandi

Alzheimer’s disease (AD) is characterized by profound metabolic dysfunction and disturbances in gut–brain axis signaling. Ketogenic diet (KD) has demonstrated metabolic and cognitive benefits in both preclinical and clinical studies. However, factors that determine individual responsiveness or non-responsiveness to KD interventions remain poorly understood. Emerging evidence suggests that gut microbiome composition plays a critical role in modulating these factors. This study examined how KD responsiveness, determined by fecal microbiota transplantation (FMT) derived from human KD responders (RES) or non-responders (nRES)- influences cognition, gut barrier function, neuroinflammation, and microbial structure in 3xTg-AD mice. We further evaluated whether supplementing KD with a novel Synbiotic Yogurt (SY) formulated by our team could augment or restore responsiveness. We hypothesized that RES microbiota would confer superior KD-driven benefits and that KD-SY would synergistically improve metabolic and neurobiological outcomes, particularly among nRES recipients. Adult 3xTg-AD mice were antibiotic-cleansed and randomized to receive Control-, RES-, or nRES – FMT, while maintained on KD for four weeks. A second cohort received KD supplemented with SY or non-fat milk along with RES- or nRES-FMT. Behavioral tests, gut permeability assay, serum inflammatory markers, brain amyloid beta (Aβ), intestinal morphology, gene expression, and 16S rRNA microbial profiling were measured. RES-FMT recipients showed early improvements in spatial memory (Y-maze and novel object recognition) and consistently lower Aβ accumulation in cortex and hippocampus. They also showed higher synaptophysin and IL-10 expression. In contrast, nRES-FMT mice exhibited distinct microbiome clustering, lower microbial diversity, enrichment of Proteobacteria, and impaired gut barrier function relative to RES-FMT recipients. Functionally, specific taxa like Enterococcus, Enterobacter, and Paenibacillus were associated with greater vulnerability to AD-related pathology, while Akkermansia, Bifidobacterium, and Muribaculum were linked with lower vulnerability. SY supplementation improved metabolic and gut barrier indices across groups characterized by increased circulating ketone levels, lowered fasting glucose and glucose-ketone index, and decreased gut permeability. nRES-SY mice showed the strongest gains in recognition memory and reductions in brain Aβ1–42 burden. SY increased expression of barrier- and inflammation-modulating genes, including occludin, APLP2, and IL-10. Microbiome analysis demonstrated higher microbial diversity and enrichment of beneficial genera such as Paralactobacillus, Eubacterium, and Muribaculum. These findings show that KD responsiveness is strongly determined by gut microbiota composition and that SY supplementation can enhance or rescue metabolic, cognitive, and microbial outcomes, particularly in nonresponders. This supports a precision-microbiome strategy combining metabolic and Synbiotic interventions to improve gut–brain axis function in AD. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.