The nature of the association between free radicals and cancer is complex and paradoxical, as it seems that free radicals and oxidative stress can induce cancer, but at the same time the transformed cells, that is, the cancer cells generate more free radicals than normal cells. Endogenous antioxidant compounds, including glutathione and lysozyme, can limit the effects of oxidative stress, but these systems can be quickly saturated by high amounts of free radicals. It is important to increase the cellular levels of antioxidants that could provide protection against possible adverse agents that can cause a cell cancer. A good diet and the knowledge of several compounds of foods with antioxidant effects may be helpful to prevent cancer disease.