There is no need to fast for a thyroid gong test because the body’s thyroid hormone levels are relatively stable throughout the day and are not affected by diet. There is no great change in thyroid hormone levels before and after eating, so fasting is not required to check thyroid function. Some patients do ask if they can check their thyroid function after they have eaten today, and the doctor tells them that they can do so. It may be more convenient for the patient to come in on an empty stomach to have their thyroid function checked, because there are often other items that need to be checked when the thyroid function is checked, such as liver function, kidney function and blood lipids, so it is more convenient to check them together.