Child Specialist Ghaziabad. Which oil should be used to cook food?Is it good to prepare food in desi ghi and butter. ? You can use the same oil which is being used to cook food for other family members. No single oi/l fat has an ideal composition, and hence a frequent change of oil between groundnut oil, mustard oil and Soya bean oil is preferred. Some people also use olive oil. If we are using the same oil repeatedly for cooking it increases the component of trans fat which is unhealthy and very harmful for the body .Thus reusing the oil that has been earlier used for flying should be avoided .Yes we can use a bit of Desi Ghee or butter in preparing food to make it healthy and palatable but we should keep the fact in mind that per day saturated fat should constitute less than 10% of the total energy intake.