It has also been demonstrated that MCT supplementation-evoked improvement in cognitive functions was observed in patients with mild to moderate Alzheimer’s disease or mild cognitive impairment without apolipoprotein E (APOE) ε4 allele [326,327], but the mechanism of action of APOE-ε4 status on MCT/ketosis-generated alleviating effects was not identified. This evidence concerns the gene APOE and Cognitive impairment.