These—in parts contradictory–findings may be explained by results obtained by multiple trajectory studies that demonstrated a greater risk for the development of dementia and AD in subjects with declining BMI in later adulthood (Gu et al., 2014; Emmerzaal et al., 2015; Alhurani et al., 2016; Cova et al., 2016), a relationship that appears to be further modified by the APOE genotype with carriers of the ε4 allele exhibiting a steeper decline of BMI (Bäckman et al., 2015). This evidence concerns the gene APOE and dementia.