https://www.ncbi.nlm.nih.gov/m/pubmed/14578137/
"In several epidemiological studies, high intakes of fruits and vegetables have been associated with a lower incidence of cancer. Theoretically, intake of antioxidants by consumption of fruits and vegetables should protect against reactive oxygen species and decrease the formation of oxidative DNA damage."
...
"Our results show that after 24 days of complete depletion of fruits and vegetables, or daily ingestion of 600 g of fruit and vegetables, or the corresponding amount of vitamins and minerals, the level of oxidative DNA damage was unchanged."
Cancer Epidemiol Biomarkers Prev. 2003 Oct;12(10):1016-22.
