Patients with inflammatory bowel disease are often malnourished, underweight, and even cachectic. According to statistics, 56%-75% of patients with inflammatory bowel disease (especially Crohn’s disease) are underweight and 60%-80% have anemia. They are deficient in basic nutrients such as amino acids (basic components of protein), glucose (carbohydrates), minerals and trace elements, vitamins and water, but the most important is protein deficiency. The most direct causes of malnutrition are inadequate intake, excessive loss and impaired absorption of dietary nutrients. The relationship between inflammatory bowel disease and dietary factors is still controversial. It has been suspected that certain foods or the dietary intake of certain harmful components, such as macromolecular compounds, bacteria or other pathogenic organisms and their antigenic components, trigger an abnormal response of the intestinal immune mechanism, causing immune damage to the gastrointestinal mucosa that is difficult to abort. Animal experiments have confirmed that even if the genetic background for the development of inflammatory bowel disease is clearly present, the disease does not develop as long as the gastrointestinal diet is not followed. There is a popular saying that “if you don’t eat, you don’t have inflammatory bowel disease (no food, no IBD)”. However, if one does not eat, there is no nutritional intake and the patient has no way to recover. Many patients in clinical practice are often afraid of “eating” because of abdominal pain, diarrhea, blood in stool, etc. after eating due to strictures, obstruction, ulcers and bleeding in the digestive tract. They think that “it is better to eat less or not to eat at all than to eat something harmful”. In some cases, due to surgery, partial removal of intestinal segments, or fistula, the amount and speed of eating is limited, and the food eaten is not completely digested and absorbed. On the other hand, during the acute activity of inflammatory bowel disease or in patients with more than moderate activity of the disease, the intestine is constantly losing blood and tissue fluid components in addition to the reduction of the absorption area due to the extent of the lesion, which affects the absorption of nutrients and vitamins and minerals, and the exudation and bleeding from the lesion. This is significantly exacerbated during active disease in patients with Crohn’s disease. Moreover, the acute activity of the disease brings about stress on organ functions and greatly increases nutritional consumption, which, combined with the effects of long-term medications such as corticosteroids and aminosalicylates, makes nutritional deficiencies an increasingly prominent problem. In addition to protein and fat, vitamin A, folic acid, zinc, calcium, potassium and magnesium are deficient to varying degrees. Patients show signs of weakness, weight loss, reduced immune function, and difficulty in wound healing. In turn, malnutrition directly affects the repair of damaged areas of the intestine. Once trapped in this vicious cycle, the patient’s condition rapidly worsens and systemic failure occurs. Similarities and differences in the nutritional management of Crohn’s disease and ulcerative colitis Crohn’s disease may affect all parts of the digestive tract, mainly the small intestine, but most commonly the distal part of the small intestine, the terminal ileum, followed by the large intestine immediately adjacent to the terminal ileum. Ulcerative colitis, on the other hand, invades essentially only the colon. Also in Crohn’s disease or ulcerative colitis, the extent of the lesion varies, as does the size of the invasion and the impact on the patient’s nutritional metabolism. In mild cases, the difference may be less than normal, while in severe cases the patient’s life may be at risk. Both Crohn’s disease and ulcerative colitis can present with impaired absorption and excessive loss of nutrients, but because small bowel lesions are seen primarily in the former, malabsorption is significantly more severe in patients with Crohn’s disease than in the latter. The small intestine is the main site of nutrient absorption. Enzymes secreted by the mucosa of the small intestine mainly break down carbohydrates, such as lactose into galactose and glucose, which are then absorbed into the bloodstream to be used by tissues and organs such as the liver. Protein is mostly digested and broken down into amino acids in the small intestine, while fat becomes fatty acids, triglycerides and cholesterol. The small intestine also secretes some proteases and lipases to break down the corresponding nutrients. All these small molecules are absorbed in the small intestine and then transported to the whole body. Iron is absorbed mainly in the upper part of the small intestine. The final small intestine is responsible for the absorption of vitamin B12, folic acid and other important hematopoietic factors. In contrast, the large intestine has a relatively simple function, mainly absorbing water that has not yet been absorbed by the small intestine. Therefore, it is not difficult to understand that in inflammatory bowel disease, especially in those with lesions in the small intestine, the digestion and absorption of these nutrients can be severe. Moreover, different parts of Crohn’s disease affect nutrient metabolism differently. Zinc deficiency can occur in both ulcerative colitis and Crohn’s disease, but zinc deficiency is more severe in Crohn’s disease, and zinc deficiency causes a much more severe condition of reduced immune function in patients. The same type of Crohn’s disease anemia can also be different. In Crohn’s disease with a predominantly terminal ileal lesion, deficiencies of vitamin B12 and folic acid can lead to megaloblastic anemia. In the case of ulcerative colitis, since the lesions are only in the large intestine, they have less impact on the digestion and absorption of nutrients in the small intestine. Therefore, the impact on nutrient metabolism is also less than in Crohn’s disease. Because of this, there are relatively few patients with ulcerative colitis who suffer from severe malnutrition, mainly due to recurrent mucus and blood stools and the development of iron deficiency anemia. We are also talking about the dietary management and nutritional support of Crohn’s disease. In order to ensure the nutrition of patients with inflammatory bowel disease while avoiding overloading the gastrointestinal tract with digestion and absorption and exacerbating inflammation, various dietary formulas and nutritional support treatments have been designed. For patients with extensive lesions, severe disease, and complications that prevent nutritional intake via the gastrointestinal diet, special diets or total parenteral nutrition (TPN) are required. The latter is a nutritional support treatment that does not go through the gastrointestinal tract at all and relies only on intravenous input. Diet and nutrition for patients in remission or mild disease Patients in remission or mild disease are those who do not have fever, have diarrhea 3 times a day or less, have no or little blood in their stools, and have normal hematocrit, sedimentation, and C-reactive protein on blood tests. Nonetheless, their dietary management should be taken very seriously. It is important to have adequate nutritional intake to ensure the repair of intestinal lesions, but also to avoid an inappropriate diet that could promote disease activity. In addition to caloric intake (about 1200 calories a day for those without physical activity), protein intake must be emphasized in order to ensure the repair of intestinal lesions. Other nutrients should not be neglected. In addition, attention should be paid to the supplementation of foods rich in folic acid, zinc, calcium and other nutrients. In a sense, most of the foods available to normal people are basically not contraindicated for patients with inflammatory bowel disease. Meat, fish, poultry and eggs, milk and dairy products provide essential proteins and other nutrients and are also suitable for them. The emphasis of the diet is not on which foods can be eaten and prevent relapse, but on how to choose and cook them and how to eat them. Patients with inflammatory bowel disease have a reduced area for digestion and absorption in their intestines. The limited area for nutrient absorption must be used to achieve the absorption of more nutrients. This places different requirements on food processing and cooking. In order to break down the ingested food, meat or vegetables into large molecules and then degrade them into small molecules to facilitate absorption, food processing must be done thoroughly and well, cooking should be simplified, and less or no coloring, spices and seasonings with no nutritional value or even harmful and irritating are used. Do not add sugar, especially refined sugar, because epidemiological surveys have shown that refined sugar is associated with the onset and activity of Crohn’s disease. The nature of well cooked food should be predominantly semi-liquid and liquid, and food or dishes should not be cooked very hard or half-cooked. Most of the stir-fried dishes are not suitable for patients with inflammatory bowel disease. Raw, semi-raw, pickled, brewed, coarse, spicy, fried, greasy, and unfresh foods and dishes need to be avoided. The diversity of disease types and the degree of intestinal involvement in patients with inflammatory bowel disease, as well as the existence of individual differences, means that it is impossible to develop a fixed diet plan that will work for all patients. Moreover, the disease itself is constantly changing, and dietary patterns must change with it. Therefore, dietary and nutritional management must have both overarching principles and must be implemented on an individualized basis. The overall principle is to achieve a balanced diet, also known as a healthy diet. It must be able to cover the daily nutritional quota required by the patient and meet all the nutritional components required by the body. Since these patients are mostly deficient in folic acid, vitamins A and D, calcium, iron and many other nutrients, it is important to choose foods rich in these nutrients. The patient’s diet should supply sufficient amount of calories and high quality proteins as well as the above mentioned related nutrients. Recipes should include different types of foods: meat, fish, poultry, dairy products (if tolerated), grains, fruits and vegetables. For example, by eating fewer and more frequent meals, once every 3-4 hours, 5 meals per day can be arranged, with the amount of each meal being a little less than the usual 3 meals per day and the duration of each meal being appropriately extended. This will help the gastrointestinal tract adapt to the food and fully digest and absorb it. If you are lactose intolerant, you should reduce your intake of milk and dairy products. High-fiber foods such as nuts, corn, and some vegetables should be appropriately limited. A low-fiber, less residue diet should be the mainstay. If the lesion is extensive and the symptoms of activity are obvious, the restriction should be more strict. High-fiber foods promote intestinal motility and can lead to diarrhea if they are not fully digested in the small intestine. However, some patients may experience post-feeding abdominal discomfort and intestinal cramps even after following the above dietary recommendations. For these patients, medication may be helpful. Antispasmodics and antidiarrheal medications taken 15-20 minutes before eating will relieve symptoms. Fruits are a major source of vitamins and other nutrients. People usually eat fruits raw. For people with inflammatory bowel disease, whether they can eat them raw or cook them before consumption needs to be treated differently. Cooking fruits before consumption is a requirement for the dietary management of Crohn’s disease. However, this also needs to be treated flexibly. We do not force all patients to cook the fruit before consumption. If the patient has obvious signs of activity, such as increased diarrhea and significant blood in the stool, then cooking must be emphasized; for those with stable disease and no basis for activity, eating fresh fruit is not strictly contraindicated. However, attention should be paid to the amount and speed of consumption, which should be less rather than more, and slower rather than faster. Another issue is how to accurately treat the issue of dietary fiber. Food fiber is not only important for normal people to promote intestinal motility, accelerate the excretion of harmful bacteria, waste and toxins, maintain intestinal micro-ecological balance and immune function, but also for patients with inflammatory bowel disease. Previously, there was a one-sided emphasis on avoiding dietary fiber in these patients, and in fact, this view is wrong. Patients with inflammatory bowel disease also need food to provide essential fiber components. The current view is that, in addition to active severe inflammatory bowel disease, patients in remission or mild disease should be encouraged to eat moderate amounts of fiber-containing foods and vegetables. Nutrition in the acute active phase should pay special attention to reducing the load on the intestinal tract, such as abdominal pain, diarrhea, blood in the stool and fever and other manifestations of patients should be fasted. At this time, if the patient’s diet remains the same and does not reduce the load on the diseased intestine, then no therapeutic measures will be effective. If necessary, oral medications should also be stopped or changed to injectable administration. At this time, the only way to supply nutrition may be to adopt total parenteral nutrition to replenish the basic nutrients required by the patient daily, or to adopt the special nutrition supply in the form of liquid nutrition by placing a nutrition tube or taking it orally, which is the so-called “space diet” or “industrially produced liquid food”, i.e. a liquid mixture composed of different formulations of various nutrients. According to the different components, they are also known as low-molecular diet, polymer diet or elemental diet. The U.S. National Space Administration (NASA) developed the space diet to address the limited space in the spacecraft, to ensure that the astronauts adequate nutritional supply. The diet is free of “rough impurities” as much as possible. The nutrients in this type of diet are smaller molecules and do not contain dietary fiber, which is quickly and completely absorbed by the upper part of the human digestive tract, leaving no residue to enter the large intestine and need to be eliminated from the body. This means that the lower part of the digestive tract, the small and large intestine, can get a complete rest, which is the key to successful liquid nutrition or tube placement nutrition therapy. The traditional space diet is no longer produced because it contains only amino acids, has an unpleasant odor, and has a poor taste. Current liquid nutrition contains low molecular nutrients containing oligopeptides and also incorporates fats and flavoring substances, which are aromatic, very palatable, and have a wide variety for patients with different conditions. (1) Liquid nutrition is implemented through the mouth or through the placement of nutrition tubes There are high molecular liquid diets and low molecular liquid diets. The former has been modified and also divided into high fiber diet, high molecular diet or high molecular diet plus medium chain fatty acid (MCT) diet, etc. The nutrients in the low-molecule diet have been broken down into simple molecules and are thus more easily and completely absorbed when they enter the gastrointestinal tract. It is also a balanced diet that also covers the patient’s daily nutritional quota and is free of fiber. Usually, the liquid diet is delivered into the duodenum via a nasogastric (intestinal) tube, which needs to be controlled by a pressure pump and infused continuously. Some low-molecular liquid diets can also be given directly by mouth. For patients who are able to take it orally, they should be encouraged to meet the basic nutritional intake by oral intake, from little to much, and gradually achieve adequate nutritional supply. Different flavors of liquid nutrition should be provided to suit the requirements of different patients. In addition, patients should be ensured to have adequate daily fluid (water) intake. The amount and rate of nutritional fluid intake and changes in abdominal symptoms and urine output should be monitored and recorded in detail. It is also important to choose a liquid diet with a certain limit on fat for a certain period of time, depending on the situation, and later, medium-chain fat can be added gradually, depending on the condition. For those who cannot tolerate a high molecular liquid diet, a low molecular liquid diet should be substituted. For those who need long-term liquid nutrition, transnasal gastrointestinal tube is usually used. Before implementation, the physician can discuss with the patient to determine whether oral nutrition at home or a gastrointestinal nutrition tube should be placed. The greatest advantage of liquid nutrition, whether given directly orally or by tube, is that it prevents atrophy of the microvilli of the small intestine and a decrease in intestinal immune function. It is recommended to start slowly and in controlled amounts, with 300-500 ml on the first day, and then gradually increase. With liquid nutrition preparations, it is possible to change the diet from regular diet to liquid nutrition without hospitalization, even if the patient’s condition deteriorates. It is important to note that liquid nutrition should not be left at room temperature for too long to avoid spoilage. Both low-molecular liquid diet and high-molecular liquid diet have been proven to have good therapeutic effects on inflammatory bowel disease. During an acute attack of ulcerative colitis, an oral liquid diet is usually sufficient, and total parenteral nutrition (TPN) is not required. If diarrhea and blood in stool are very serious, or if symptoms worsen after oral liquid nutrition, total parenteral nutrition must be implemented. (2) Total parenteral nutrition is generally used for patients who fail to receive oral or transoral tube nutrition, have lesions in the upper gastrointestinal tract, especially in the upper small intestine, small intestine obstruction, scar formation or leaky tube affecting nutrition input (e.g. rectovaginal fistula), and patients with short bowel syndrome due to extensive small intestine surgical resection. Total gastroenteric parenteral nutrition is administered through central venous cannula (CVC), where nutrients and active ingredients are fed directly into the bloodstream as a liquid. Thus, the body’s stomach and intestines are completely rested. However, this way of nutrition supply has advantages and disadvantages. On the one hand, the patient’s gastrointestinal tract is completely rested for a short period of time, and inflammation and its associated symptoms are rapidly restored. On the other hand, the gastrointestinal tract becomes “lazy” as a result, i.e., the gastrointestinal mucosa becomes disused and atrophies in form and function occur. At this point, the original digestive and absorptive functions take some time to recover. The duration of total parenteral nutrition or enteral nutrition is determined according to the patient’s condition. As long as the indicators related to intestinal inflammation such as diarrhea and other subjective symptoms of the patient remain abnormal, total parenteral or enteral nutrition should be continued. However, total parenteral nutrition should be stopped as soon as possible and the oral nutrition intake should be gradually resumed. This process can be started by cross-over for a few days, i.e., decreasing intravenous nutrition and starting oral low or high molecular nutrition solution at the same time. The duration of total parenteral nutrition or special enteral nutrition supply should last at least 2-4 weeks. If the patient’s symptoms remain unrelieved, continued avoidance of food is also required. (3) How to transition to normal diet after acute activity After the patient’s general condition improves, the transition to normal diet should be considered gradually. At first, the patient can eat some drinks, cereals and a small amount of bread. If the patient is able to tolerate it, further cooked fruits and vegetables, potatoes, rice or pasta paste, low-fat cheese, luncheon and lean meats, poultry or fish, etc. are given. Finally, more fat, cheese or meat is added. At this point, the patient is ready for a normal diet. A light diet (LND) may also be given during hospitalization, depending on the condition and systemic situation. When configuring a light diet, avoid choosing foods and cooking processes that are intolerable to the patient. The light diet may not need to be continued after discharge from the hospital, but it is also important to avoid foods and cooking processes that are not tolerated by the patient at home. For the first few days, do not immediately give the patient adequate energy, and do not hastily withdraw parenteral or enteral nutrition; it may be combined or crossed over at the same time to avoid weight loss. When transitioning to a normal diet, pay attention to the time rhythm and do not rush. The fiber component can be increased only after the disease has improved. During this time, a thorough and detailed plan should be developed in close cooperation between the patient, the physician, the dietitian, and the hospital nutrition department. Patients should maintain permanent contact with their physicians and dietitians so that information is always available. Frequent attention should be paid to the patient’s heart, liver and kidney function, etc., as the function of these organs is related to the nutritional elements in the diet. When communicating and discussing nutrition with patients, consider vitamin, mineral, and micronutrient supplementation. Patients should also take the opportunity to discuss with their physician and dietitian to develop a diet that is appropriate for them. A few things patients need to do 1. Keep a disease diary and a diet diary Managing inflammatory bowel disease well requires a long-term collaboration between the patient, the doctor and the dietitian. Since most patients do not live in the hospital or occasionally stay in the hospital for treatment of flare-ups. Therefore, it is important for patients and their families to monitor their condition during the time they are away from the hospital and to have records that truly reflect objective changes in their condition. Only when this is done can the doctor fully grasp the changes in the patient’s condition and come up with just the right individualized and rational treatment plan for the patient’s illness. The contents of the diary should reflect the changes in the patient’s condition and nutritional status. Therefore, the signs and symptoms related to the condition and the record of medications taken are the most important parts, and the other part is the record of diet and nutrition. (1) Body temperature was measured twice daily, before breakfast and one hour after lunch. (2) Abdominal pain, bloating, abdominal masses and bowel sounds and their relationship to diet. This is used to reflect the activity of the disease, the presence or absence of intestinal strictures and obstruction, and the tolerance of the gastrointestinal tract to the food consumed. (3) The number, nature and amount of stools, and the relationship between stools and diet. Be specific about what kind of food is eaten at each meal, whether it is meat, poultry and eggs or some kind of fruit and its beverage or what kind of vegetables. There should also be a specific method of cooking. If blood in the stool is present, describe the color, amount, and odor. (4) Measure the weight once a day. The time is specified to wake up in the morning (6-7 o’clock), urinate once (no stool), not eat anything, and dress (weight) consistently. The diet diary helps patients to accurately measure their intake of calories, protein, and vitamins and other nutritional elements. 2. The meaning and method of accurate weight measurement Weight is an important indicator of nutritional status and development. Patients with good nutritional status are more able to tolerate the damage caused by disease and inflammation to the organism. If the weight is insufficient, during acute relapse, the patient will lose more weight, making the lesion more difficult to repair. Therefore, patients with inflammatory bowel disease should maintain a normal or near-normal weight (calculated as the ratio of height to weight) as much as possible, and not less than 20% of the standard weight. Some patients may exceed the normal weight standard. If they are mildly overweight (e.g., 10%), they do not need to lose weight through a restrictive diet. These patients are more fortunate to have more energy stores for repair or to cope with more exertion. Normal weight is generally calculated using Broca’s index, i.e. height (cm) – 100 = weight (kg). The reduced value should be within 20% of normal. This formula is applicable to a height of 160-190 cm. The calculated value (theoretical value) may be high if the upper and lower limits are exceeded or lowered. When applied in practice, slight changes should be made. Another weight calculation method is the body mass index (BMI). Its formula is: BMI = weight (kg)/height (m).2 The upper and lower limits of normal values are 18 and 25, respectively. 3. Find the cause and solve the problem of food intolerance Improper diet can promote or aggravate inflammatory bowel disease. The problem is that it is not possible to identify and tell which food or its preparation is intolerant to a particular patient and which food causes symptoms of discomfort such as abdominal pain, bloating and diarrhea. Some articles list a number of possible intolerances such as soy products, raw vegetables, fruit juices (especially lemon juice), citrus juices (oranges, oranges, lemons, etc.), onions, fatty foods, acidic foods, milk (lactose intolerance), and dairy products. Every patient reacts differently to food, but it is important not to fear and resist certain foods without basis. This is not conducive to nutritional intake. Therefore, the solution is for patients to be mindful of their own observations and to seek out and identify the foods they cannot tolerate. We strongly advocate that patients keep a good diary of their diet for use in addressing food intolerances. The diary should be maintained over time. It should include the time of all meals (eaten or drunk), the type of food or drink, subjective feelings and symptoms after eating, especially discomfort such as abdominal pain and diarrhea. The number and nature of the daily stools, as well as their color, should be recorded in detail. As long as the patient does this, you will quickly discover after a few weeks what foods are intolerable and remove such foods from your repertoire to avoid triggering disease activity. Of course, you can also try the above-mentioned foods again after a few weeks, especially after your condition has significantly improved. Some foods can be changed from intolerable to tolerable when the disease improves. After an acute attack, it is important to start with foods that were tolerated when the patient resumes eating. Well-cooked meat, fish, rice or pasta paste, cooked fruits and vegetables should all be tolerated. The diet should be varied, covering bread, omelets, butter, jam, honey, meat, poultry, fish, and cheese. If there is no discomfort after a few days, new foods can be added. Add one variety every 2-3 days. If there is still no problem, indicating tolerance, you can continue adding more new varieties. It is important to note that one or more discomforts may occur with reduced doses of corticosteroids. At this point, do not mistake it for food intolerance. 4. Be proactive in keeping in touch with your own physician and dietitian Patients with inflammatory bowel disease are all different. Even for a specific patient, the condition changes from one period to the next. This requires constant adjustment of the patient’s medication and dietary management. There should be open and frequent communication between the patient and the physician (including the dietitian) to exchange information in a timely manner. Patients should reflect their condition and dietary management to their doctors accurately and promptly without fear of trouble, and monitor the relevant indicators regularly or irregularly; doctors should take the trouble to continuously guide patients in dietary management, nutritional intake and medication according to the changes of their condition.