The difference between animal fat and vegetable oil is that vegetable oil is composed mostly of polyunsaturated fats, which are missing more than one pair of hydrogens in its structure, while animal fat is composed mostly of monounsaturated fats, which are missing only a single pair of hydrogen, and saturated fats, as claimed by Dr. Mercola. Saturated and monounsaturated fats are more easily accessible and usable by the body in comparison to polyunsaturated fats. Saturated fats have all of their hydrogen atoms in place, which causes them to form a straight chain and is the reason behind why animal fats are generally solids at room temperature; however, unsaturated fats, whether it be polyunsaturated or monounsaturated fats, have kinks and bends in their molecular structure, which is why they tend to be liquid at room temperature, like vegetable oil.
The U.S. Department of Agriculture recommends consuming either polyunsaturated or monounsaturated fats rather than saturated fats, as they contain fatty acids that are essential in maintaining good health.
Research has also shown that the unsaturated fats that are found in vegetable oil do not raise bad cholesterol, and are a major source of vitamin E, which also offers numerous health benefits to the body. Although fatty acids are essential to one's health, it is important to limit one's intake.