fats are used to absorb or get nutrients, like fat-soluble vitamins for humans. it is used as a source of backup energy in cases when carbohydrates are not available, or people can not use it at that time. people need more than 20 to 35% of daily calories from fat. also, fats play a role in helping people's body maintain or keep the core (center) temperature. however, they are also harmful, in other words, they have bad effects on human's bodies.