When people just feel hungry, their bodies will consume fat. The specific duration varies from person to person, and there is no fixed standard. (Unless you are extremely hungry and exhausted, you will choose to destroy the organization and let protein participate in the energy supply process. )

Conventional methods are glycogen decomposition, fat decomposition and white matter decomposition, but what you are talking about is a state of chronic hunger, which means that people have entered a state of decomposing protein, because without energy supplement, people are a function. No matter what you do, you need energy to maintain it, that is, it is always consumed, just like a car is on fire. No matter whether it's going up the waves to refuel or down the waves to save fuel, oil is always needed to maintain the state.

Extended data:

The metabolic characteristics of starvation process regulated by hormones such as insulin decrease and glucagon increase are as follows:

① Muscle decomposition is strengthened, and most of the released amino acids are converted into alanine and glutamine.

② The gluconeogenesis was enhanced. Alanine is regulated by glucagon in the liver, which significantly accelerates gluconeogenesis. Glutamine formed by muscle is absorbed by intestinal mucosa and converted into alanine, which enters the liver through portal vein and is another source of gluconeogenesis. It can be seen that gluconeogenesis mainly occurs in the liver (about 80% of gluconeogenesis, and the rest 20% in the renal cortex).

③ The decomposition of fat is accelerated, and the contents of glycerol and fatty acids in plasma are increased. As a result, gluconeogenesis has been strengthened. Glycerol can directly generate sugar, while fatty acids can provide energy for gluconeogenesis, generate acetyl coenzyme A, and promote gluconeogenesis of amino acids, pyruvate and lactic acid. About 1/4 of fatty acids decomposed by fat are converted into ketone bodies in the liver, so plasma ketone bodies can increase hundreds of times when hungry. Fatty acids and ketone bodies become the energy sources of myocardium, renal cortex and skeletal muscle, and some ketone bodies can also be used by the brain.

④ The decrease of glucose utilization in tissues is due to the oxidation of tissues and the strengthening of fatty acids and ketone bodies. The physiological significance is to reduce the limited source of glucose and turn to fat storage, because the body stores far more fat than glycogen. It can be seen that when you are hungry, the gluconeogenesis is strengthened, and the utilization of glucose is reduced, which is beneficial to maintaining blood sugar levels and maintaining the functions of the brain and central nervous system. It is worth noting that due to the strong adaptability of myocardium to the utilization of nutrients, myocardium turns to use high concentration ketone bodies in blood in time when it is hungry, thus effectively protecting itself physiologically.

In the process of hunger, due to the drastic changes in biochemical metabolism, the human body will inevitably produce body fat consumption and muscle decomposition, which will lead to emaciation and fatigue. Physiologically necessary heat energy mainly comes from the decomposition of fat (accounting for more than 80%) and protein, and ketone bodies in blood will rise, which may lead to ketosis and acidosis. Supplementing glucose to hungry patients is a "timely help", which can not only prevent ketosis and acidosis, but also save 50g muscle protein per 100g glucose.

Be broken down into fuel.

References:

Baidu encyclopedia-hunger