Sudden weight loss in chronic colitis is often caused by a decrease in the digestive and absorptive function of the gastrointestinal tract. Chronic colitis is due to a variety of reasons that cause the colon to have a chronic inflammatory disease, often leading to inflammatory edema, congestion, erosion of the intestinal mucosa, which leads to a decline in intestinal function, affecting the absorption of food, and after the intake of food, the nutrients are not able to be adequately absorbed, which will lead to weight loss. In particular, chronic colitis, if not treated in time, may lead to gradual aggravation of the condition, often diarrhea, abdominal pain, mucus stools, pus and blood stools, and may be accompanied by fecal incontinence, resulting in weight loss. Sudden weight loss in patients with chronic colitis indicates that the condition is more serious, and it is important to consult a doctor in a timely manner and cooperate with the doctor’s treatment.