All fats are high in calories, but saturated fat and trans fat raise the "bad" LDL cholesterol in your blood and can cause plaque to build up in your arteries. This can lead to heart attack or stroke. Hard margarine, butter, and shortening all have these bad fats. To keep your heart healthy, choose oils instead. Olive, canola, corn, and safflower oils contain the least saturated fat.
Saturated fats need to be limited to 10% of calories, so most of the time choose heart-healthy oils instead.