Exercise on an empty stomach is very harmful. The source of human energy is mainly carbohydrates (sugar) ingested in the diet. After a night's rest, the energy consumption in the body is almost the same, and the blood sugar concentration in the body is low. At this time, if we exercise without eating anything, we will consume a lot of energy and our blood sugar concentration will be lower. Blood sugar is the direct energy substance of the brain. If the blood sugar concentration is too low, the brain will feel tired because of lack of motivation, people will feel dizzy and weak, and some people will look pale and break out in a cold sweat. If it continues, it will be unconscious, even unconscious.

Another disadvantage of taking part in sports on an empty stomach is that when people are empty, the main source of energy is transformed and supplied by body fat. At this time, the free fatty acids in the blood will increase significantly. Fatty acids are the source of energy for muscle activities such as myocardium, but when used in excessive amounts, they can become the poison of myocardium, causing various arrhythmias and even sudden death.