Cancer patients can eat onion, which contains vitamins and minerals of other common vegetables, and also has certain effect of lowering blood pressure and blood fat. Many cancer patients do not have a good appetite, especially after radiotherapy and chemotherapy, some of them will have gastrointestinal reactions, so eating onions can promote the appetite of cancer patients and increase their nutrition. Besides, onion also contains allicin, which has a certain antiseptic and anti-inflammatory effect. However, onion should not be eaten too much, as it may cause flatulence and gastrointestinal discomfort, especially when the gastrointestinal function of cancer patients is not very good, onion should be eaten as little as possible.