Whole grains including oats are concentrated sources of antioxidants, substances that delay the onset or slow down the rate of oxidation in the body. Oats are good sources of compounds with vitamin E activity, including tocotrienols. Grains contain more tocotrienols than other food products. Tocotrienols have vitamin E activity but are also inhibitors of cholesterol synthesis and have been found to lower serum cholesterol. Whole grains are also good suppliers of selenium, copper, zinc, and manganese, which function as antioxidants.
Grains also contain phenolic acids and phytate, which are known antioxidants.
Antioxidants in grains may contribute to a health benefit since antioxidants are thought to decrease the risk of cancer and cataracts, as well as aging. Free radicals produced during the oxidation process are involved in disease processes and antioxidants can prevent or delay their formation. Whole grains also contain phytoestrogens, which have been linked to decreased risk of hormone-related diseases such as breast cancer. Epidemiological data support that breast cancer is positively related to early menarche, late menopause, nulliparity and delayed first pregnancy. Populations at low risk for developing breast cancer have been found to have high intake of phytoestrogens, compounds in plants that have estrogenic activity in humans.