Vegetables, fruit, and cancer. I. Epidemiology.
This review article analyzed 137 studies on the association between fruit and vegetable consumption and cancer. In these studies, the consumption of higher levels of fruits and vegetables was associated with a reduced risk of cancer. This association was found for a wide variety of vegetables and fruit. Furthermore, the protective effects were more consistent for raw forms of fruits and vegetables. Further details can be found in the study.
Steinmetz KA, Potter JD. Vegetables, fruit, and cancer. I. Epidemiology. Cancer Causes Control. 1991 Sep;2(5):325-57.