The incidence of malnutrition in Crohn’s disease (CD) is about 50%-80%, and according to the statistical results of complex CD admitted to our department, the incidence of malnutrition is 86.7%. Patients in the active phase often show weight loss and hypoproteinemia due to infection, restricted diet, fever, etc. Patients in remission may show obesity and metabolic bone disease due to the effect of drugs, etc. In recent years, the incidence of CD in China has increased significantly, and it is of great clinical importance to carefully understand and master the treatment of CD. The causes of CD malnutrition include three main categories: insufficient intake, excessive consumption and loss, and drug side effects. CD patients often restrict their dietary intake on their own due to abdominal pain, abdominal distension, nausea and vomiting, intestinal obstruction and other gastrointestinal symptoms that affect eating; as factors such as refined sugar, food antigens and ultra-microscopic particles are considered as possible mechanisms in the pathogenesis of CD, many foods are considered unfit for consumption, especially high-protein foods, such as aquatic products category, dairy products, etc., making the scope of patient’s intake significantly narrowed, and patients before eating Patients often have to ask, “Can I eat this? Many drugs have a negative effect on the patient’s appetite, especially 5-aminosalicylic acid, which can cause loss of appetite, nausea and vomiting, and greatly affect the patient’s food intake. Patients with active CD are often in a high catabolic state due to inflammation, infection, surgical treatment, etc. A large amount of energy and protein stores are used for fever, response to infection, synthesis of acute phase proteins and tissue repair, and nutritional consumption increases significantly. The longer the duration of the disease and the more severe the disease, the faster the depletion of the body’s nutritional reserves. At the same time, due to the formation of intestinal inflammation, ulcers, fistulas and perforations, a large amount of digestive fluid, including water, electrolytes, trace elements, digestive enzymes, hormones, and various immunoglobulins, inflammatory cells and plasma proteins are lost along with diarrhea, vomiting and leaking digestive fluid, aggravating the deterioration of nutritional status. About half of all CD patients will require at least one surgical procedure during their lifetime. In these patients with surgical complications, there are obvious obstacles to nutritional intake: some patients have external or internal fistulas, which lead to a large loss of digestive juices and affect the digestion and absorption of food, resulting in malnutrition; some patients have a significant reduction in the length of the intestinal tube, a significant decrease in the quality of the intestinal tube, and a significant deficiency in the absorption area of the intestine due to severe disease, extensive lesions, and frequent bowel resections, resulting in clinical manifestations of short bowel syndrome, resulting in or aggravating malnutrition. The nutritional consumption of CD patients in remission is less than that in the active phase. In addition to the influence of the functional state of the intestine, the nutritional status is also influenced by the therapeutic drugs, the most influential of which is glucocorticoids. It is well known that glucocorticoids can promote protein catabolism, leading to a series of metabolic complications such as abnormal sugar and fat metabolism and osteoporosis. Long-term use of glucocorticoids not only fails to maintain CD remission, but also can cause deterioration of nutritional status and should be avoided. Malnutrition is significantly associated with the outcome of CD treatment. In non-surgical patients, malnutrition impedes ulcer healing, increases morbidity and mortality from infectious complications, and decreases the patient’s quality of life. Hypoproteinemia is a high risk factor for surgical complications, leading not only to poor incisional healing and incisional hernia, but also to rupture of the intestinal anastomosis and the formation of intestinal fistulas. Malnutrition also decreases the immune function of the body, increases the incidence of complications such as abdominal infections, pulmonary and incisional infections, prolongs the hospital stay and increases mortality. Because most CD patients are malnourished and have a history of long-term use of glucocorticoids and immunosuppressive drugs, the morbidity and mortality of complications are significantly higher if surgery is performed, which is an important reason why many surgeons are reluctant to treat CD patients. Due to the recognition of the impact of malnutrition on the outcome of CD treatment, emphasis has been placed on nutritional support for CD. In the 1970s and 1980s, considering that intestinal food antigens might be associated with the development of CD, it was expected that fasting, intestinal rest, and total parenteral nutrition (TPN) would allow the intestine to avoid exposure to food antigens and thus allow intestinal inflammation to be alleviated. The results of the study were encouraging: some patients with CD who had failed to respond to drug therapy were put into remission by nutritional support, and the effect of nutritional support on CD was studied by a randomized controlled approach: Greenberg divided the patients into three groups: the TPN group, the total enteral nutrition (TEN) group, and the PN + oral diet group, and after 1 year of treatment the remission rates of the three groups reached The remission rates in the three groups reached 42%, 55% and 56% after 1 year of treatment, respectively, indicating that the mode of nutritional support did not affect the 1-year remission rate of CD, and that both EN and PN were effective, and even the same therapeutic effect as TPN could be achieved with a general diet on top of nutritional support. The results of this study suggest that the mechanism of action of nutritional support-induced CD remission is not fasting, which may imply some therapeutic effect. Since both EN and PN are effective, EN should be preferred, and for this reason, O’Morain conducted a well-known study comparing the therapeutic effect of the elemental diet and glucocorticoids on the inflammatory response to CD. The results showed that after 3 months of treatment, both groups of patients on the elemental diet and glucocorticoids had a significantly reduced inflammatory response, as evidenced by slower blood sedimentation and lower inflammatory response scores, with no significant difference between the two groups, and the elemental diet was similar to glucocorticoid-induced CD remission (60-80% remission rate at 3 months of use). This is quite a satisfactory treatment effect for patients treated with conventional therapies. Moreover, compared to surgical treatment and glucocorticoids, nutritional support has no side effects and is not only safe to use, but also induces CD remission while significantly improving the patient’s nutritional status, which is not possible with any other treatment. Is there any difference in the effectiveness of enteral nutrition in the treatment of CD between the elemental and non-elemental diets? Which one is better? How to choose? In order to answer this question, Rigaud conducted a controlled study in which two groups of patients were administered a combination diet and a non-component diet, and the remission rate of CD was observed after 6 weeks. After extensive clinical observations, it is now believed that the therapeutic effect of EN-induced CD remission is inferior to that of glucocorticoids, but it has its unique advantages: no serious complications and can be extended indefinitely; it can improve the nutritional status of patients while treating CD; EN can promote intestinal mucosa repair and can adjust the intestinal flora. Remove refers to the removal of suspected food pathogens that induce disease, such as allergenic proteins, refined sugars, certain fats, pathogenic microorganisms and parasites, etc., through EN instead of ordinary diet; replace refers to the provision of sufficient nutrients such as the three major nutrients, dietary fiber, vitamins and trace elements to the organism through EN to compensate for the patient’s inadequate nutritional intake; reinoculate refers to through the stimulation of intestinal peristalsis by EN to achieve the purpose of adjusting the intestinal flora gradient, at the same time, can also be given from the intestinal probiotics, such as Lactobacillus acidophilus and Lactobacillus bulgaricus, etc., to maintain the normal intestinal flora; repair refers to the direct nutrition of the intestinal mucosa through EN. EN direct nutritional effect on intestinal mucosa, providing raw materials for intestinal mucosa repair (glutamine, pantothenic acid, zinc, fructose, oligosaccharides, vitamin C, etc.), promoting the repair of intestinal mucosal epithelium and reducing the release of inflammatory mediators. It has been shown that the 1-year recurrence rate of CD patients with structural destruction of intestinal mucosa reaches 76-81%, while the 1-year recurrence rate of patients with intact intestinal mucosa is even less than 5%. As in adults, the incidence of CD in children is also increasing year by year. According to statistics, 1/4 of IBD patients are under 18 years old, and CD is the most common among them. Malnutrition seriously affects the growth and development of adolescents, and active and effective nutritional support can prevent growth retardation or stagnation in adolescents, so nutritional support is considered as the primary therapy for adolescents with CD in Europe and Japan, and EN is recommended as the first-line treatment for patients with active CD combined with growth retardation. In order to improve the success rate of surgical treatment of CD, our department has widely adopted nutritional support therapy for CD patients requiring surgery, and has retrospectively analyzed and summarized the results of surgical treatment in 150 CD patients, of which 140 were successful, 10 had surgery-related complications, resulting in 2 deaths. Our findings suggest that perioperative malnutrition is a common complication of CD and that aggressive perioperative nutritional support has positive implications for improving the success rate of surgical treatment and improving prognosis. EN not only has the effect of inducing remission in active CD, but also has the effect of maintaining remission.Dupont conducted a meta-analysis on the role of EN in maintaining remission in CD, and the results showed that after induction of remission in CD by pharmacological or surgical resection, the addition of EN orally along with normal feeding had the effect of significantly prolonging the duration of remission in CD.EN can be used alone or in combination with EN can be used alone or in combination with other drugs that maintain CD remission. The pathogenesis of CD is related to the inflammatory response and immune dysfunction. The ability of fish oil to reduce the inflammatory response and immunosuppression has been used in the treatment of CD with good therapeutic results. amre analyzed the dietary structure of 130 children with CD over a 1-year period and found that fish oil intake was negatively associated with the incidence of CD, with a decreased risk of CD in those with a high n-3:n-6 diet, suggesting that increasing dietary fish oil intake can help reduce the risk of CD development. Therefore, many scholars have tried to give oral fish oil to patients with CD or ulcerative colitis (UC), and most studies have achieved more satisfactory results. For example, after Brunborg gave 21 patients with CD and 17 patients with UC oral fish oil for 14 days, the patients had a significant decrease in blood n-6/n-3 ratio, a reduction in arthralgia, and a decrease in disease activity, although the results were not significantly different, but taking fish oil, the patients’ blood LTB4 levels decreased significantly. It can be expected that the clinical treatment effect should be more significant if fish oil is taken for a long period of time, but at this stage, due to the differences in administration, dose, observation time and other aspects, the study has not yet reached a consistent conclusion, and a large sample of randomized controlled studies is still needed. In conclusion, the treatment of CD requires multidisciplinary cooperation, of which nutritional support is one of the important tools. Nutrition is not only supportive but also therapeutic, which can not only improve the nutritional status of patients, correct malnutrition, improve the safety of surgical treatment and treatment success rate, but also induce symptomatic remission and prolong the remission period. The importance of pharmacological nutrients, especially fish oil, which has the effect of reducing the degree of inflammatory response and modulating immune function, in the treatment of CD should draw our attention. Proper use of nutrition can dramatically improve the therapeutic outcome of CD.