Very few people know that oil contains saturated fats, monosaturated fats and polyunsaturated fats. Every time you heat the same oil over and over again, its use can be harmful to your health. Therefore, avoid using the same oil over and over again. Very few people know that oil contains saturated fats, monosaturated fats and polyunsaturated fats. Every time you heat the same oil over and over again, its use can be harmful to your health. So avoid using the same oil over and over again.