Significant genotype–dietary fat interactions for obesity traits have also been reported for the apolipoprotein genes that regulate lipid metabolism (APOA1, APOA2, APOA5, APOB) [38–40], confirming previously observed GEI: the APOA2–saturated fat interaction on body weight and the protective effect of the APO5-1131 C minor allele on obesity in individuals on high-fat diets [39–41]. Here, APOA1 is linked to obesity due to melanocortin 4 receptor deficiency.