Diet and cancer research has been sparse for a number of reasons. One major reason is that reliable studies are not feasible to undertake with humans for obvious ethical reasons. Additionally, observational studies cannot show cause and effect. We are then left with animal studies that more than likely cannot be extrapolated to human cancers. In the past, only individual nutrients have been studied, i.e., vitamins, minerals, antioxidants). Studies with supplements have shown mixed results and doses are varied. Several studies using the antioxidant, beta carotene, resulted with more cases of lung cancer in smokers when compared with a placebo group. Diet patterns like the Mediterranean or vegetarian diets are difficult to conduct on large groups of human subjects due to cost.
Research on a flavonoid called sulforaphane in cruciferous vegetables may be prudent, since these compounds called phytonutrients may hold the key to cancer prevention with diet. A study from the Journal of the National Cancer Institute showed that a high intake of broccoli greatly reduced the risk of aggressive prostate cancer.