Alzheimer's disease (AD) is a common age-related neurodegenerative disorder with extremely low drug development success rates, making nutritional intervention a promising strategy. Cerebral energy metabolism dysfunction is a core pathological feature of AD. Odd-chain fatty acids (OCFAs) can generate propionyl-CoA via β-oxidation to replenish the impaired tricarboxylic acid (TCA) cycle. This study characterized the lipid composition of OCFAs-enriched algal oil by UPC2-Q-TOF-MS, evaluated its neuroprotective effects on Caenorhabditis elegans (C. elegans) models with AD, Parkinson's disease (PD), and Huntington's disease (HD), and explored the metabolic mechanism of its key component pentadecanoic acid (C15:0) using untargeted metabolomics. Results showed that triglycerides (TAGs) represented the predominant lipid class, accounting for 97.3% of the total lipid content in the algal oil. Among all the identified TAG molecular species, TAGs containing C15:0/C17:0 accounted for more than 90%. OCFAs-enriched algal oil exhibited disease-selective neuroprotection. It significantly improved locomotor function in AD nematodes, moderately ameliorated PD-related deficits, whereas showed no efficacy in HD nematodes. Metabolomics revealed that C15:0 produced propionyl-CoA to rescue TCA cycle dysfunction and energy deficits, upregulated membrane phospholipids to repair membrane integrity, and reduced abnormal metabolites to restore metabolic homeostasis. KEGG analysis confirmed that C15:0 globally regulated core metabolic pathways including amino acid, cofactor, nucleotide, and carbon metabolism. OCFAs-enriched algal oil exerted selective anti-AD effects by repairing energy metabolism, remodeling membrane phospholipids, and restoring metabolic homeostasis, providing a novel nutritional candidate for AD intervention.