A Multimodal Framework for Alzheimer's Prevention: Diet, Exercise, Fasting, Sleep, and Gut Microbiota.

Alzheimer's Disease (AD) and related dementias arise from a multifactorial interplay of genetic susceptibility, metabolic dysfunction, neuroinflammation, and lifestyle determinants. With limited disease-modifying pharmacotherapies, lifestyle interventions have emerged as compelling, evidence-based avenues for prevention and early management. This review integrates mechanistic, translational, and clinical insights on major modifiable behaviours, physical activity, diet, intermittent fasting, sleep regulation, and gut-microbiome-based approaches that collectively shape cognitive ageing. Aerobic, anaerobic, and resistance exercises exert neuroprotective effects by activating BDNF-TrkB signalling, enhancing hippocampal neurogenesis, improving synaptic plasticity, and stimulating peripheral myokines (CTSB, IGF-1, GPLD1) that cross the blood-brain barrier to support neuronal resilience. Dietary interventions such as the Mediterranean, Mediterranean- DASH Intervention for Neurodegenerative Delay (MIND), and ketogenic diets mitigate AD pathology by reducing oxidative stress, inhibiting Aβ deposition, improving mitochondrial efficiency, and modulating APOE4-linked metabolic vulnerability. Intermittent fasting induces a metabolic shift toward ketone utilisation, activates autophagy pathways (AMPK, SIRT3, Nrf2), remodels the gut microbiome, and promotes angiogenesis through GDF11 signalling. The gut-brain axis contributes to cognitive health through microbial metabolites, such as Short-Chain Fatty Acids (SCFAs), tryptophan derivatives, modulation of neuroinflammation, and enhanced neuronal survival. Meanwhile, sleep quality, particularly slow-wave sleep, optimises glymphatic clearance and prevents the pathological accumulation of Aβ and tau. Collectively, the evidence suggests that multidomain lifestyle approaches offer synergistic benefits that exceed those of individual interventions, representing promising strategies for delaying cognitive decline. However, gaps remain regarding dose-response relationships, personalised protocols for APOE4 carriers, and long-term validation in diverse populations. Strengthening these research directions is crucial for integrating lifestyle medicine into preventive neurology and public health frameworks.