Western diet, rich in cholesterol, fat and sugar, may significantly increase the risk of Alzheimer's disease in people who carry a gene linked to the neurodegenerative disorder, a new study warns. ApoE4 and ApoE3 are two variants of a gene that codes for a protein, apolipoprotein E, which binds fats and cholesterol to transport them to the body's lymphatic and circulatory systems and to the brain.