Usually, it is best to have a clinical test for trace elements on an empty stomach, but some tests for basic elements of calcium, zinc and iron do not require fasting. Trace elements are checked daily by checking blood and hair to determine the trace elements in the body. For blood test, if you eat food rich in trace elements, it will affect the accuracy of this value, commonly known as blood test contamination, so you need to fast. At present, domestic technology can check the level of trace elements in the body through hair, armpit hair, beard, and other body hairs. Since the activity of hair is relatively low, trace elements are more stable and reliable, and it is not easy to have pre-sample contamination. Usually, different parts of the hair and different segments of the hair are examined and finally evaluated comprehensively so that they are not affected by diet and other aspects of the disease. This test is more reliable and the trace elements are more balanced and will not suddenly increase or decrease because of what you eat, so there is no need for fasting tests. For some infants and young children, the test can also be done through the nails, which is less damaging to the body, does not require blood sampling, and can effectively check the indicators of calcium, iron, aluminum, and copper elements. In conclusion, fasting is required for measuring trace elements through blood tests, while fasting is not required for other testing methods.