Alzheimer's disease (AD) is increasingly linked to metabolic and microbial dysregulations, with butyrate and β-hydroxybutyrate (BHB) identified as key modulators. BHB is a ketone body primarily produced by the liver during periods of low glucose availability, and BHB levels are reduced in the AD brain and peripheral blood. Butyrate, a microbiota-derived short-chain fatty acid, is also reduced in the peripheral blood in association with gut microbiota dysbiosis. The reduction of butyrate and BHB, together with gut microbiota dysbiosis, is commonly observed in AD patients and correlates with cognitive decline and AD-related pathologies. Reduced levels of butyrate and BHB may impair energy metabolism, exacerbating amyloid-beta (Aβ) and tau pathologies. In contrast, preliminary evidence from interventional and ketogenic studies suggests that increasing butyrate and BHB levels may attenuate AD-related pathologies, such as Aβ and tau abnormalities, while improving cognitive function. Emerging evidence suggests that both butyrate and BHB can cross the blood-brain barrier (BBB), suppressing oxidative stress and pro-inflammatory cytokines and potentially mitigating Aβ aggregation and tau hyperphosphorylation. Accordingly, therapeutic strategies targeting the microbiota-butyrate-BHB axis represent a promising and biologically plausible approach that warrants further rigorous clinical investigation for the prevention and treatment of AD. This review comprehensively examines the roles of butyrate and BHB in ameliorating key AD-related pathologies, including Aβ aggregation, tau hyperphosphorylation, neuroinflammation, and neurodegeneration. Additionally, the review explores the bidirectional association between butyrate/BHB and gut dysbiosis in AD, including how dysbiosis reduces butyrate/BHB levels while elevating them may reverse dysbiosis and improve gut-brain axis function. Collectively, these findings suggest that butyrate and BHB emerge as promising candidates for potential novel adjunctive therapies for AD, although supporting human evidence remains preliminary and heterogeneous.
