Dietary Patterns, Micronutrient Adequacy, and Metabolic Vulnerability in Alzheimer's Disease: A Critical Narrative Review.

Dietary factors may influence cognitive aging and Alzheimer's disease (AD), but observational associations, mechanistic findings, and intervention effects should not be considered equivalent evidence. This critical narrative review examines how dietary patterns, micronutrient adequacy, and metabolic health may modify AD-related vulnerability. A targeted search of PubMed/MEDLINE, Scopus, and Web of Science through April 2026 prioritized systematic reviews, meta-analyses, randomized trials, and prospective cohorts. Mediterranean, Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND), and healthful plant-based dietary patterns have been associated with better cognitive outcomes and lower dementia risk. However, evidence remains predominantly observational, and randomized trials have not consistently demonstrated prevention of cognitive decline. Strict vegan diets have not shown additional protection beyond high-quality plant-based diets and require careful attention to vitamin B12 and overall nutritional adequacy. Ketogenic diets and medium-chain triglycerides may increase cerebral ketone availability, but their cognitive benefits remain inconsistent, and disease modification has not been established. Although vitamin B12, folate, and vitamin D support neural and metabolic functions, correcting deficiency should not be equated with treating AD. Overall, nutrition should be viewed as a contributor to cardiometabolic and neurological resilience and as part of person-centered dementia care, rather than as a stand-alone disease-modifying therapy. Future studies should integrate accurate dietary assessment, objective adherence measures, metabolic phenotyping, AD biomarkers, and clinically meaningful outcomes.