Modern nutrition tells us that the energy for human activity comes mainly from carbohydrates and fats in food, while the structure and function of the human body depends mainly on proteins, which are synthesized by the body using amino acids from food. In addition, the body needs very small but vital amounts of minerals and vitamins to maintain normal functioning. All of these require us to eat every day and take in from our food. Because of food safety concerns, many people, including organized businesses and research institutions, envision replacing three meals a day with purified nutrients, or even simply not having to eat. It is not technically difficult to simply administer various nutrients from a vein, except that it requires venipuncture or deep vein placement. Intravenous infusion of nutrients has been practiced for many years in clinical settings for patients whose GI tract cannot tolerate food or nutrients. The theory seems to be that eating only pure nutrients or pure intravenous nutrient input is not a problem, as long as people can forget what once tasted good and resist the temptation of food. But this seemingly okay theory ignores the interests of a group that cannot be ignored: the intestinal flora that live at the bottom of the food chain, begging for a living in the stinking human colon. These flora are with us from birth until old age. There are no bacteria in the fetal intestine, and after birth, after passing through the mother’s birth canal, the bacteria from the birth canal are swallowed by the baby and become the first intestinal flora. After birth, after breastfeeding and contact with the surrounding environment, more flora is admitted. During the first three months when the infant’s immune system defaults to itself for everything it comes in contact with, these bacteria become colonized and flourish here until adulthood. Gut flora can stay in the gut for a long time and not be removed because the immune system is tolerant to them and does not initiate an inflammatory response to destroy them. And more importantly, they are good for our health. While some of the food we consume every day is indigestible by the body itself, bacteria have enzymes that can digest these substances and provide extra energy to the body. Perhaps in a subsistence society these energies are insignificant and rather detrimental to weight loss, but in times of famine these energies are not extra, they are life-or-death decisions. Without intestinal bacteria, the acquisition of vitamins B and K would also be problematic. Also the intestinal flora forms a barrier against other foreign bacteria. In patients who have been on broad-spectrum antibiotics for a long time, the intestinal flora is disrupted, and germs that would not normally thrive can cause serious infections. The intestinal flora are beneficial, not because they are ecumenical, of course, but because they are also the beneficiaries. The residues left after food is digested and absorbed, and the large number of cells that die in the intestine every day, seemingly useless to the body, are a delicious treat for bacteria. Although people despise their own intestines, often using the metaphor of a sewer, they are the iron rice bowl of intestinal bacteria. Compared to some of their bloodless counterparts, such as Vibrio cholerae, Clostridium botulinum, etc., the normal flora of the intestinal tract seems to be more comfortable and less passionate, but they enjoy a comfortable and productive life because of their successful cooperation with the human body. Going back to the opening hypothesis, if people eat only nutrients every day, and assuming that these pure nutrients are so qualified that they are all absorbed in the stomach and small intestine, without any residue reaching the large intestine, then the intestinal flora, which would have needed a lot of food residues to survive, would starve. Some bacteria are simply starved to death, while others turn into an inactive budding state like a gold-digging woman who refuses to bear children for her low-income husband. Within the first few days, people will feel very uncomfortable, such as headaches, nausea and vomiting, and heartburn. This is caused by the death of a large number of intestinal bacteria and the release of endotoxins from the bacteria being absorbed. Not all bacteria will die, but under normal circumstances various bacteria maintain the ratio is the result of the struggle to kill each other, when some bacteria starve to death, some other bacteria instead because of less competition and soar, and this condition developed bacteria are often not friendly to the human body. Just like the original need for a lot of hard labor in the city suddenly all mechanized, honest hard labor will be unable to find work and starve to death, while some hard labor had to switch to bandits. So, eating pure nutrients or intravenous nutrition may seem highly sophisticated, but it is not suitable for our human body. It is like transferring the utopian social model hard to a country where everyone is running for food and clothing and there will be internal and external problems at times. The mutual use of humans and bacteria is not to demonstrate the harmony between humans and nature, but a long-term evolutionary result that does not work that way. What if we didn’t have to worry about bacteria? Although they have coexisted with humans for millions of years, but after all, they are not my kind of people will be different, in fact, even if the medical name of the normal intestinal flora, there is no lack of human weakness or immune system dysfunction, taking advantage of the well to take advantage of the fire guys. Hypothetically, only hypothetically, there really is such a future, there is no bacteria in the world, is it possible to not eat? I’m afraid not, because it is difficult for the human body to accept such a huge change. The human body digests food by relying on a large amount of liquid secreted by the digestive tract, some of which is strongly acidic and some alkaline, and which contains various digestive enzymes. Digestive juices are secreted in large quantities when a person eats, or even when he or she is ready to eat. Even when not eating, digestive juices will continue to be secreted in small amounts. Our digestive tract is essentially no different from the food we eat in that it is composed of biological macromolecules, and the same digestive juices that can digest food can also digest our own tissues. Under normal circumstances, digestive juices are used to digest food, while the inner surface of the digestive tract also secretes a lot of mucus to protect itself. If there is not enough food to “neutralize” the digestive juices, and if mucus production is reduced, the juices can damage our own digestive tract, especially if it is already damaged. Starvation can aggravate peptic ulcers, and patients with bleeding peptic ulcers used to be prevented from eating, but it has been found that starting to eat early is good for ulcer healing. In addition to digestive juices, our liver secretes a lot of bile to help with the absorption of fats. The liver secretes bile in a completely planned economy, and it does not care how much the market needs, it just secretes that much every day. Even if it is not needed, or even if the bile output channel is blocked, it will continue to secrete. What is not used temporarily is temporarily stored in the gallbladder, and when it is needed, the cells of the gastrointestinal tract will inform the gallbladder to output bile by secreting cholecystokinin. If one keeps not eating, the bile keeps storing. The capacity of the gallbladder is very limited, so it can only concentrate the bile, and when the concentration limit is exceeded gallstones are formed. Therefore, the incidence of gallstones is significantly higher among those who control their diet in order to lose weight. In conclusion, although we now have a variety of pure nutrient products, and even intravenous nutrients that do not require direct injection into the bloodstream via the mouth, we should continue to eat, both from an economic and a health perspective.