Usually patients with diarrhea can consume vitamin C in moderation. The main causes of diarrhea are intestinal infection, improper diet, gastrointestinal dysfunction due to cold, and indigestion, while vitamin C is formed by antibodies and collagen, which can maintain the body’s immune function and enhance the patient’s constitution to resist infection and relieve diarrhea. Vitamin C from dietary sources is widely found in fresh vegetables and fruits, such as bitter melon, tomatoes, citrus and peaches. When vitamin C-rich foods are consumed, the vitamin C in them is generally absorbed in the duodenum and upper jejunum, a small amount is absorbed by the mucous membrane in the stomach and mouth, and the unabsorbed vitamin C is transmitted directly to the large intestine. A moderate amount of vitamin C supplementation can activate the bacteria that exist in the intestinal tract with effective effects and adjust the function of the intestines and stomach, which in turn may effectively relieve the symptoms of diarrhea and prevent its aggravation. However, care should be taken not to consume too much, so as not to increase the burden on the gastrointestinal tract and aggravate the diarrhea. Moreover, no matter how much vitamin C is consumed, the effective intestinal absorption will not change depending on the total amount consumed, and any excess vitamin C will be decomposed by microorganisms in the intestine to form gaseous substances. When there is too much gas in the abdominal cavity, not only will it not relieve diarrhea, but also bloating will occur, aggravating the patient’s discomfort.