Fat or lipids are substances mostly found in animal-origin food, though they are also found in vegetable species. There are many types of fat, divided according to their molecular structure into simple, composite and derived lipids. Simple lipids are the most commonly found in our body and our diet.The best known are triglycerides. Composite lipids are triglycerides combined with other chemical substances. Derived lipids are the result of simple or composite lipid transformation, the most important being cholesterol.