APOE and Mental deterioration: According to the animal study, mice having ApoE ε3 and ε4 did not show distinguishable cognitive decline based on water maze behavior task, but when fed HFD for 6 months, mice having ApoE ε4 showed significant cognitive decline compared to mice having ApoE ε3 fed HFD, representing the importance of the brain metabolism as an environment factor to the cognition [45].