The emptying time of food in the stomach is related to the type of food. Because no matter what kind of food, the emptying time in the stomach is about 3-5 hours. Simple carbohydrate food can only stay in the stomach for more than three hours because of its simple structure and easy digestion and absorption. Protein and fat can stay in the stomach for more than four hours because of their complex structure and slow decomposition, which is why eating meat can resist hunger.

Once the stomach is empty, there is only gastric juice left in the stomach, and the stomach growls with peristalsis, suggesting that we need to eat. At this time, it also shows that the nutrition and energy provided by the last meal have been exhausted by the human body and need to be supplemented with nutrition.

Liver glycogen can provide energy for human body in a short time. When the energy provided by food is exhausted, that is, after blood sugar is consumed, glycogen will be released to provide short-term energy supply for the human body. Hepatic glycogen is a small amount of energy stored in the liver, which can provide short-term energy supplement for the human body. Glycogen release is a so-called phenomenon that we often encounter in our daily life, but it lasts for a short time. When glycogen is consumed, hypoglycemia will occur, and symptoms such as irritability, fatigue and inattention will appear. If you don't eat, you will consume protein and fat stored in your body.

Protein and fat break down into glucose to provide energy for human body, which is called "gluconeogenesis". It is often discussed whether protein or fat breaks down first to provide energy for human body in hunger. In fact, both of them began to decompose at the same time, and there is no order, but the amount is different in different time warp. After fat catabolism, it produces metabolites such as water, carbon dioxide and ketone bodies, which provide energy for human body. However, if ketone bodies are produced too much, it will cause ketoacidosis and cause harm to human body, so in the process of losing weight, we can't pursue too fast.