In addition to making people feel hollow in the abdomen and having a desire to eat, it also causes a series of reactions of important organs such as the brain, liver, pancreas, and kidneys. Here we simply understand these reactions and their effects on health.

　　In addition to making people feel hollow in the abdomen and having a desire to eat, it also causes a series of reactions in important organs such as the brain, liver, pancreas, and kidneys. In order to let everyone understand these reactions and their impact on health, we set a simplified scenario: a healthy adult, who has been eating normally for several years, and after eating a normal lunch (12 o''clock) on a certain day, no longer Eat and go hungry. During this period, Ta''s physical activity was as usual, with no illness, trauma or other accidents. Let''s take a look at the reactions of important organs in his body (the time limits of "4 hours" and "10 hours" in the following are not absolute and are only approximate reference times; the weights of "15 grams" and "90 grams" are not accurate. Measured, only a rough reference number)

　　Early hunger:

　　After 5pm (after 4 and 5 hours of lunch), the digestion and absorption of lunch foods (especially sugar), Blood glucose (glucose in the blood) drops to pre-meal levels, at which time there are a total of 3 or 5 grams of glucose in the blood. Organs such as the brain and muscles continue to consume glucose, and blood sugar tends to continue to decline. If the blood sugar level is too low (hypoglycemia), the brain will be difficult to work properly (blood sugar is almost the only energy source of nerve tissue), so the body will make the following adjustments to maintain blood sugar stability:

　　①Muscle cells stop Ingest blood glucose and instead use the glycogen stored in the muscle (about 180-300 grams in total).

　　②The liver cells decompose the glycogen (about 70-100 grams in total) stored in it into glucose and output it as blood glucose, which is mainly provided to the brain for use.

　　③Heart, kidney, liver and other energy-consuming organs mainly use oxidized fatty acids as energy sources and rarely consume glucose.

　　 In short, the energy consumption during this period is mainly glycogen (reserved during normal diet), muscle glycogen supplies muscles, and liver glycogen supplies the brain (and a few tissues such as red blood cells). Other organs use fatty acids as energy sources.

　　Hunger continues:

　　The next morning (after another dozen hours), glycogen (especially liver glycogen) is exhausted (the weight of the liver has decreased, muscles have decreased The weight has also decreased), blood sugar is facing the risk of being too low again, in order to avoid hypoglycemia from affecting the brain''s work, the body makes the following adjustments again:

　　①The liver cells start to synthesize glucose by themselves, and the raw materials are some Sugar substances such as glycerin (from fat breakdown) and amino acids (from muscle protein breakdown). Among them, 10-15 grams of glucose is synthesized using glycerol (in 24 hours), and 90-120 grams of glucose is synthesized using amino acids (in 24 hours).

　　②Kidney can also synthesize glucose, but its output is lower than that of liver.

　　 ③ Muscle, heart, kidney, liver, etc. further reduce the consumption of glucose (mainly fatty acid consumption), to "save" glucose and supply the brain (and a few tissues such as red blood cells).

　　 ④The mitochondria of liver cells also use fatty acid metabolites (acetyl-CoA) to synthesize "ketone bodies" (acetone, acetoacetic acid and β-hydroxybutyric acid). Ketone bodies are transported by the blood to the heart, kidneys, muscles, brain, etc. for energy use.

　　Continue hunger (do not eat or eat very little)

　　①The liver continues to synthesize glucose, and the kidney''s synthetic glucose production also increases, supplying glucose to the brain.

　　②Muscle protein is forced to break down continuously, and its product is amino acid, which is the main raw material for the synthesis of glucose. The result of losing the car (muscle) and keeping the handsome (brain) is that the muscle weight is reduced and the weight is reduced. Theoretically, 90-120 g of glucose needs to consume 180-200 g of protein (amino acid). Muscle protein breakdown, and possibly visceral protein breakdown, will have a very bad impact on life. To this end, the brain makes adaptive adjustments.

　　③The brain uses ketone bodies (synthesized directly from the liver, and indirectly from lipolysis) as the main energy source to save glucose, and thus save muscle or visceral proteins (amino acids). The daily consumption of protein (amino acid) is about 35 grams.

　　All in all, in the early stages of starvation, the glycogen stored in the body is quickly depleted, and muscle protein is decomposed, because glycogen and muscle have a large amount of water, combining 2 and 4 times their own weight of water, Therefore, the weight will be significantly reduced, giving the illusion of weight loss. Starvation continues, and the body turns to increase fat (and ketone) utilization to slow down muscle breakdown. Fat provides more energy, has a very low water content, and loses weight more slowly.