Although almost everyone knows that full exercise is not good, there are two completely different views on fasting exercise. Many dieters and bodybuilders support running on an empty stomach. Indeed, because the blood sugar content in the body is low on an empty stomach, the ratio of running energy to fat will increase at this time, so more fat can be consumed. However, this is also the problem. Because the blood sugar level in the human body is low on an empty stomach, and blood sugar is the only source of brain energy, running on an empty stomach will further reduce the blood sugar content, which will make the brain lack the necessary energy source and easily lead to hypoglycemia such as dizziness, limb weakness and even syncope. Although free fatty acids in blood can be the energy source of muscles such as myocardium, the utilization efficiency of fatty acids in myocardium is not very high. Excessive fatty acids may cause various arrhythmias. In history, several famous middle-aged and elderly joggers died suddenly while exercising on an empty stomach (of course, there is an age problem here). On the other hand, due to insufficient sugar content, some fats will not be completely oxidized, and eventually some ketone bodies will be generated, while too many ketone bodies in the body will easily cause acidosis. In addition, fasting exercise is easy to make people feel hungry, and may also cause abdominal pain, which affects people's normal digestive function. For the above reasons, I suggest you don't exercise on an empty stomach. If you are used to exercise on an empty stomach, such as running in the morning, you can supplement a small amount of carbohydrates and liquids before exercise, such as fruit and vegetable juice and drinks made of honey. This is especially true for middle-aged and elderly people, because there are many middle-aged and elderly people with hypertension and diabetes. Due to age and physical factors, their ability to use fatty acids is lower than that of young people, so they should try to avoid fasting exercise.