Unhealthy dietary patterns and Alzheimer's disease: associations and underlying mechanistic pathways.

Unhealthy dietary patterns are increasingly recognized as important modifiable factors associated with cognitive decline and Alzheimer's disease (AD). Diets characterized by high intake of saturated fats, refined sugars, and ultra-processed foods are consistently linked to metabolic dysfunction, systemic inflammation, and impaired brain health. Epidemiological and interventional studies suggest that these dietary patterns are associated with poorer cognitive outcomes, whereas adherence to nutrient-rich dietary patterns such as the Mediterranean, MIND, and DASH diets is linked to improved metabolic profiles and slower cognitive decline. Several biological mechanisms have been proposed to explain these associations, including insulin resistance, oxidative stress, neuroinflammation, vascular dysfunction, and alterations in gut-brain axis signaling; however, much of the current human evidence remains observational, limiting definitive causal inference. Emerging research also indicates that individual susceptibility to diet-related AD risk may be modified by genetic background, metabolic status, and sex-specific biological factors. Despite variability in study findings, the overall body of evidence supports a biologically plausible relationship between dietary quality and key processes implicated in AD pathogenesis. Future research should prioritize long-term, biomarker-driven randomized controlled trials, alongside life-course approaches that consider early- and mid-life dietary exposures, to better clarify causal pathways and inform targeted nutritional strategies for AD risk reduction.