A fatty diet turns down the genes that move fats around in normal mice, but not in mice that don’t have the ApoE gene.

When mice eat a fatty diet, the genes that make brain fats shut down in normal mice and ApoE4 mice—but not in mice that have no ApoE gene at all.

When mice with the ApoE4 gene eat a fatty, cholesterol-rich diet, their brains accumulate more saturated fats than when they eat normal food.