Aim Adherence to the Mediterranean‐dietary approaches to stop hypertension (DASH) intervention for neurodegenerative delay (MIND) diet has been associated with a reduced risk of dementia, yet clinical and mechanistic evidence is limited. This study aims to explore the relationship between MIND diet adherence and cognitive function in Alzheimer's disease (AD), with a specific focus on resting‐state EEG to investigate the underlying mechanisms. Methods We evaluated 841 memory clinic participants: 119 cognitively normal, 255 with mild cognitive impairment, and 467 with AD. Cognitive, dietary, neuropsychiatric, and functional data were collected. EEG from 204 participants was analyzed for spectral and connectivity features. Results MIND scores were significantly lower in the AD group ( P < 0.001). Higher MIND adherence was linked to better global cognition, lower dementia severity, fewer mood symptoms, and greater daily functioning ( P < 0.05). Individuals in the lowest adherence tertile had 6.78 times higher odds of cognitive impairment compared to those in the highest tertile (OR = 6.78, 95% CI: 4.54–10.13, P < 0.001). EEG analyses revealed that greater MIND adherence was associated with increased alpha power, reduced occipital theta/beta and delta/alpha ratios, and stronger frontoparietal connectivity. Mediation analysis indicated that frontal and global alpha power partially mediated the associations between MIND diet adherence and dementia severity, mood symptoms, and functional status. Conclusions High MIND adherence is associated with improved cognitive and functional outcomes in AD. EEG signatures may partially mediate these effects, highlighting the clinical potential of the MIND diet for early intervention and neurophysiological monitoring.