We eat a lot of food every day to metabolize and sustain our life, but food is more than just nutrition for us. Our gastrointestinal tract is composed of the stomach, small intestine, large intestine and digestive glands. Food digestion is accomplished through mechanical and chemical digestion, and the digested nutrients enter the blood and lymphatic supply through the walls of the digestive tract. In addition to digestion, absorption and excretion, the gastrointestinal tract also has neuro-endocrine and immune-defense functions, and food can affect these functions. First of all, there are more than 40 kinds of endocrine cells isolated from the gastrointestinal and pancreatic glands, which are distributed in the mucosal layer from the bottom of the stomach to the large intestine. The total number of gastrointestinal endocrine cells is so large that it is estimated to be more than the sum of cells of other endocrine glands in the body (such as thyroid, pituitary, adrenal, gonad, etc.), so the digestive tract is not only the digestive organ in the body, but also the largest and most complex endocrine organ in the body. The hormones secreted by it are called gastrointestinal hormones, which can coordinate the digestive, metabolic and endocrine functions of the body. Some gastrointestinal hormones, besides existing in the gastrointestinal tract, also exist in the brain tissue, and the peptides originally thought to exist only in the brain are also found in the gastrointestinal, pancreatic and other digestive organs, and this dual distribution of peptides is called brain-gut peptides. The function of brain-intestinal peptides in the brain is being extensively studied, for example, it was found that the cerebral cortex contains high concentrations of cholecystokinin, and injection of cholecystokinin into the brain of animals can significantly inhibit the intake of food and produce the so-called satiety-inducing effect. Patients with certain neurological and psychiatric diseases (such as Alzheimer’s and schizophrenia) have altered levels of some brain D-intestinal peptides in brain tissue and cerebrospinal fluid. Various peptides in the nervous system may be involved in the regulation of activities such as feeding, body temperature, metabolism, pain, and memory of behavior, hence the gastrointestinal tract is known as the “gut brain”. Patients with depression often have symptoms of gastrointestinal dysfunction, such as belching, abdominal pain, bloating, diarrhea, constipation, and so on. Research has found that certain ingredients and metabolites in food have brain D intestinal peptide-like effects, which can regulate the human gastrointestinal tract function, mood, mental state, etc. That is why some foods can calm the mind, and some foods can stimulate the peristalsis of the stomach and intestines. Secondly, the lymphatic tissue of the gastrointestinal tract accounts for more than 1/3 of the lymphatic tissue of the whole body and produces 75% of the body’s secretory antibodies, which is considered to be the largest immune organ of the body. The gastrointestinal tract requires a large GI surface and thin epithelial cells to absorb nutrients while being exposed to a large number of food antigens and microorganisms, leading to the generation of associated immune responses. In the upper intestine, most antigens are exposed from the chyme, while in the ileum and colon, a large and complex community of commensal microorganisms loads additional antigens. The barrier action of the GI epithelium does not completely resist the entry of antigens from the GI tract into the tissues. Although the immune system is constantly sampling GI antigens through epithelial cells and dendritic cells, the GI epithelial barrier is a highly mobile structure that limits but does not reject antigen entry into the tissues. Thus, non-destructive food antigens can be found in plasma and some GI bacteria are found in the mesenteric lymph nodes of healthy animals, and different food foods can influence the composition of the flora. Thus food may play a role in the pathogenesis of many diseases. With improved living and hygiene conditions, the vast majority of infectious diseases of the GI tract are under control, however, the occurrence of gastrointestinal food antigens and spontaneous inflammation is growing rapidly; in other words, we are now developing inflammation without being infected. Although the cause is still unknown, the idea is being recognized that underlying GI infections disrupt the balance between normal bacteria and compromise the immune system of a healthy GI tract and mucosa. Healthy individuals have an abundant and highly active GI immune system that prevents excessive immune responses to food and GI bacteria. It is now believed that inflammatory bowel disease is caused by a genetic defect in the patient that leads to a deficiency in immune function and an imbalance in mucosal homeostasis, resulting in an inappropriate and sustained inflammatory response to the normally present intestinal flora and food antigens, where food influences the development of inflammatory bowel disease by affecting antigen production, the composition of the intestinal flora and possibly the neuroendocrine system.