2. Lettuce leaves contain a variety of nutrients, including protein, fat, sugar, ash, provitamin A, vitamin B 1, vitamin B2, vitamin C, calcium, phosphorus, iron, potassium, magnesium, silicon and other trace elements and dietary fiber, so it can promote the development of bones, hair and skin and contribute to human growth. Recent studies have found that lettuce leaves contain an aromatic hydrocarbon hydroxylated fat, which can decompose nitrosamines, a carcinogen in food, and prevent the formation of cancer cells. It has a certain preventive effect on liver cancer and gastric cancer of digestive system, and can also alleviate the reaction of cancer patients to radiotherapy or chemotherapy.