Effects of ketogenic diet on cognitive impairment in older adults: a systematic review and meta-analysis.

BACKGROUND: Cognitive impairment in older adults is associated with substantial functional decline and care burden. The ketogenic diet (KD) may improve cognition, but evidence in older adults with cognitive impairment remains inconsistent. This study evaluated the effects of KD, including related ketogenic dietary strategies, on cognitive outcomes and metabolic markers. METHODS: PubMed, Web of Science, Embase, the Cochrane Library, CNKI, Wanfang, and VIP were searched from inception to July 2025 for randomized controlled trials of KD or related ketogenic dietary strategies in older adults with cognitive impairment. Two reviewers independently screened studies, extracted data, and assessed risk of bias. Meta-analysis was performed using Review Manager 5.4. RESULTS: Twelve randomized controlled trials involving 707 participants were included. Compared with control interventions, KD-related dietary strategies improved overall cognitive function [SMD = 0.34, 95% CI (0.16 to 0.52), p < 0.01]. Domain-specific analyses showed significant improvements in memory [SMD = 0.53, 95% CI (0.10 to 0.96), p = 0.01] and language function [SMD = 0.43, 95% CI (0.16 to 0.70), p = 0.002], whereas no significant effects were observed for attention or executive function. KD-related strategies increased acetoacetate and β-hydroxybutyrate concentrations, indicating effective ketone production. Regarding metabolic safety, KD-related interventions increased total cholesterol and LDL-C, while triglycerides and HDL-C remained unchanged. CONCLUSIONS: KD and related ketogenic dietary strategies may improve cognitive performance and enhance ketone body production in older adults with mild cognitive impairment or Alzheimer's disease. The potential metabolic implications associated with lipid changes should be considered alongside cognitive benefits.