Vegetable oils or even fish oils provide a source of fat and fat helps either put on weight or provide energy. In fact, most fats provide at least twice as much digestible energy (used for all body functions) than protein. That is why a small amount of fat or oil goes a long way.
Paraffin oil is non-digestible, therefore doesn't provide anything for the body's use. It has previously been used to try to help prevent sand colic, however it's not been shown to be very effective.
Licensed Veterinary Technician