There are a few different categories of fat: saturated, unsaturated, monosaturated, polyunsaturated, and trans fat. You want to stay away from trans fats and you don't want to eat too many saturated fats, but there are healthy fats out there. Olives, olive oils, fatty fish, walnuts, and avocado are all healthy forms of fat. A small amount of grass-fed beef isn't the end of the world either, so long as it isn't pumped full of hormones.